Yes, it would be rude for her to have him stay over without your permission (especially if she didn't change the sheets -ewww). But if you are fine with it (and I assume you are since you let her brother do it) then next time, tell her it's fine but you don't want them using your bed.  

I think it would be pretty obvious if someone has been sleeping in your bed and hasn't changed the sheets.  I too would consider this extremely rude to do this without your permission.  One's own bed is about the most private area of a house, and woe betide anyone who dared to sleep in my bed without me saying they could.  It would be a very long time before they got another invite to my place. 

And say why. I did this in my home when I was a single mom and had a similar situation. None of the almost adult children would own up to it. I also kept my alcohol in my bedroom closet and it gave me security knowing that at least it wasn't accessible when I was traveling. One of my sons had the nerve to say something about my locked door and I said why would you need access to anything in my room when I'm out of town ;) 

This is one of those weird situations.

On one hand, she is 24 and can do what she wants when it comes to dating.

On the other- you don't want anyone else having sex in your bed... and who would want to have sex in their parents bed, that's weird. 

I agree with locking your room next time, I wouldn't really say anything to her about it if you ever want a housesitter again. Just wash your bedding when you get home and don't think about the rest. 

Sleeping in someone's bed is a boundary that she shouldn't be crossing without permission.  

I think her dad should have a talk with her that he has noticed the bed is in a different condition than when he left.. did she sleep there or allow someone else to sleep in his bed?  That it's not something he wants to see happen in the future and wanted to clarify that.  

Other option involves a lock for the bedroom door... locked while you are gone and there is no temptation.

It may be she had friends over and they slept there too... I wouldn't be happy with it.

Ew, I can't stand the idea of anyone sleeping in my bed and not changing the sheets. 

Thats a hard line. No to sleeping in your bed alone or otherwise.

I would go absolutely effin' nuclear on her. NOBODY has sex in my bed other than me and dh. NOBODY. And I don't give a monkey's whether she changed the sheets or not because she has already DEFILED MY PERSONAL PRIVATE PLACE.

And, in the highly unlikely possibility that she didn't go anywhere near my bed, by going nuclear on her ensures she never, ever tries to risk it. 

We have left my SD (24) to house sit for a week whilst we are on holiday. I made her up the single futon in the spare room. 

It would not bother me. I would have expected SD to sleep in our bed if we were not home and she was house sitting. I would have expected her to sleep in the comfortable bed.  As to the BF, she's 24. They were alone. I'd have been amazed if he didn't stay over. 

I'd be pissed about the bed but not necessarily the boyfriend. If you made up the futon and told her to sleep there, she should have slept there. Boyfriend or not. And yes, two young and motivated people can share a single bed, couch, or futon. Or the floor. Or he could sleep elsewhere. I deeply value the privacy of my bed. 

I am so sorry you were violated in this way. It is beyond rude and disrespectful. Hopefully she will not be "house sitting" in the future!

We installed cameras a while back at the suggestion of a great friend who had similar problems as yourself, and I am telling you, I have had NO ISSUES. I can see everything, at any time of day or night. I have a time stamp, a date, everything! It gives you a COMPLETE picture and digital documentation of EVERYTHING.

You can find many online, some are hidden, or appear to be regular objects that wouldn't arouse suspicion. For me personally, I wanted them to be VISIBLE so there was no two ways about it, YOU COME HERE, YOU WILL BE WATCHED! It uploads to The Cloud also, so I can pull up anything stored at anytime. 

Your husband is never going to believe your word against his princess', but when you have living proof and he can see his surroundings, he will quickly become a believer.

I'm tech savvy, but you don't really need to be. One of the best ones I've seen is ZMODO. I had to set up a private secure network for them, but I have complete peace of mind knowing my phone alerts me if there is ANY MOVEMENT, even birds or trees blowing in the wind. 

They're also very useful if you hire someone to house sit, or water plants and feed pets and your paying them to do so. You can  see if they're really doing it or not!

Do it as soon as you can!