With adult SD's it comes down to expecting basic human decency.  Barring extenuating circumstances (like you were the other woman who wrecked their relationship)...there should be an expectation that you are able to be civil to one another.

things you might say?

I know it must be difficult for you.. dealing with the fact that your parent's relationship didn't work out.  Hopefully you can at least take some lessons from their situation to live your life the way you think it should be.   I wasn't there and don't know the details.  However, I love your father very much and I'm fairly certain that at the root of it all, we all want the same thing for your father.. to be happy.  I believe that your father and I ARE happy together.  I'm sorry if that is difficult for you to accept.  I have no intention of trying to replace your mother in your life, but I am your father's partner.  We don't have to love each other, shoot, we don't even really have to like each other, but we both care about the same man and we owe it to him to act civilly because in the end, he is the one most hurt when we can't get along.  I am also perfectly happy to give you space to maintain your relationship with your dad.  If you are interested in getting to know me better and developing a relationship with me.. I am also open to that, but it isn't a condition that is going to be forced on you.  The only thing that is expected is that we display common courtesy towards one another when we are at the same place.

What does your DH have to say about all of this?

If you feel the need to respond, I would do it via email and CC your DH on it. He doesn't get to be on the sidelines while his daughters treat you with disrespect. If it weren't for him, you wouldn't even know them. He needs to set his daughters' straight and demand that they either respect you or not contact you, and continued disrespect will result in him not being around, either.

I don't know what her email said, so I can't exactly give you talking points other than to respond with, if you need to, "I'm sorry you feel that way". Nothing irritates someone trying to pick a fight more than when you shut down the fight. As tempting as it is to engage, shutting it down and walking away will accomplish far more.

i don’t spend my time engaging with crazy people in public places.   I don’t defend myself nor argue with them.  I certainly don’t engage in emails or texts.

Likewise I do not deal with my SOs crazy ex in any fashion, and block her from every way known to man that she might try to contact me.

It sounds in your situation envoking the crazy person rule might be a good plan.  You aren’t going to change these bitter skids no matter what you say or do.  But ignoring them gets their goat.  So just continue doing more of that.  If your DH doesn’t like it, he can have a talk with them.  But you don’t need to be involved.

like

What did the email say? Does it require a response, or is ignoring the best tactic?

Had you been around during her visit, you still would have ruined it.

Although you have a lot to say, it would most likely go unheard or get twisted. If she confronts you and starts yelling at you, just walk away and let her be the crazy person. They really do hate it when others don't engage in their drama.

Where is your husband in all of this? Has he seen the hateful email?

My SD27 has not ever truly been hateful to me. She has tried to sneak in a snarky comment here and there and I pretended not to even hear her. First of all, she really is not worth it, second, I knew it was disappointing for her, as I knew it took a lot for her to muster up the courage, and she probably thought she was clever (which she is not)... all to go unnoticed. Out of the corner of my eye, I could see her looking at me for a reaction. All of that effort, on her part, for nothing!

Also, she probably wanted me to say something snarky back so she could then look to her dad for support and protection from her mean 'ol step mom. A disappointing day for her, all around.

There is no point telling her what you've got on your chest because she doesn't care and she'll only use it as ammunition against you. 

If she starts yelling, just say "I will NOT be spoken to like that" as firmly as you can and walk away. Yoiu don't have to stand there and take it. If she follows you around yelling, "Talk to me when you've calmed down. I'm used to dealing with adults." and get into your car and drive away.

Forward the letter to DH and CC her, and add " Dear DH, this is between you and SD, YOU FIX THIS!" 

It's almost comical how complaints from disgruntled adult skids are exactly the same just tweak a detail here and there. 

• Wants him and whatever resources he has all to themselves.
• He doesn't need a woman in his life because his children and grands should be enough.  
• SM is abusive, wicked and brainwashing their poor unwitting father with her hoo hoo.
• SM needs to go!

How to deal?  Know that it isn't personal or about you, skids would hate anyone he was with.  Leave emotion out of your interactions with them.  Pretend they are clients of DH's, act professional and let him deal with them.  Forward all correspondence to him then promptly block them, and let him see them outside of your joint home since you are so horrible. 

If SD does catch you off guard with a screaming fit just give her a blank stare and confused look then go and get her father.  There is no defending yourself against these unwarranted attacks since they have nothing to do with you.  

You will not be visiting my home anymore.  If you can’t respect me, stay at a hotel.  You are not going to change SD’s. Do not even try. Just makes you look weak and desperate.  There are the ones who disengage, not you. 

Ignore the whore(s).   Just tell your DH to keep them away from you. Block them every which way you can.   Just erase them 100% from your life. 

That’s what I have done. It works beautifully.  

Sounds like SD loves her self-induced pity parties.  What a childish, irrational and hateful email rant.  Don't waste anymore energy on it. It's futile to try and beat crazy people at their own game of delusional crazymaking.  

Ignore, disengage and distance yourself emotionally. This puts you in control and thwarts her ability to get a rise out of you. Happy, sane SMs are those who are unwilling to be bogged down by SD's whining and mud-wallowing.  

I do hope you continue to set strong boundaries and don't sell yourself short in this area. It's really up to DH to put SD in her place and demand acceptable behavior. YOU decide when and where you’ll engage with SD if at all.  Stick to your guns and keep boundaries in place when she tries to encroach upon them. She will.  Stay assertive and aware with protecting yourself from anymore SD poison...this way you won't be caught off guard.

And...have a wonderful evening knowing that you have really gotten under SD's jealous, green skin. Lol. 

My middle-aged SDs always said they did not get along with their mother either. But that is so they can keep dad wrapped around their fingers.  They know how to play one off the other.   After several years of marriage, BM is the one you can tell they want to keep happy.

I've been through all the crap you are talking about. You cannot reason with this jealous type. I tried appeasing my OSD telling her I did not want to come in between her relationship with her dad (even though she is married with children). There is nothing that you can say other than you are leaving that will make them happy. My OSD thinks that her father was supposed to move by her to help her care for her children.  Yours may think the same.

If I have one regret, it's the extent I tried to smooth things over when I was not the one with the problem in the first place. I lowered myself when there was no need to.

So the best thing is to say nothing and leave your DH to handle it. Tell him you are sorry his family is not accepting of the marriage. You deserve to live your life in peace and will continue to do so.