I would have probably said something too. I remember being a teenager and going to a friends house. She was so rude to her mother that it really made me look at her differently from then onwards. Often parents reap what they sow. If they tolerate it then it becomes the norm. I hate it when parents do not realize that kids need rules and boundaries and that without them they just keep escalating their behavior until they find a boundary (be it a teacher at school or the law).

your SD sounds like mine - I never say anything, she once called me names and she never did again, I think she still regrets calling me a whore..... I do not care how she talks to SO or BM, not my kid not my problem...

We are never with her in public lol,

My skids treat DH and I MUCH better than they do their BM.

DH downloaded a parental monitoring app on skids electronic devices, shows all text messages, filters web browsing etc. The night we put it on them SD13 was especially upset and she was texting BM basically chewing her out and text yelling at her. If I hadn't seen it with my own eyes I NEVER would have believed SD13 acted/said those things. It was so different to how she treats DH and I, I am very thankful for that

Sounds like my sister's kids when they were teenagers. When my DD would come home from a visit with them, she would come home with that same nasty attitude. She'd say something disrespectful once, testing me, and I always passed the test. Took only the one time and I had my well-behaved daughter back. Not saying she was/is perfect, but I would not tolerate the blatant disrespect.

I wouldn't have had the nerve to call my parents names.

Kids push and test boundaries all the time. It becomes especially bad with teenagers.

That's how they know that they are protected, safe and loved, when they get pushed back, not when they are allowed to do/say whatever they want.