We have a live in aide and she wants to go out on Friday and Saturday nights. She does not come home until 5 am. Can we set a curfew?

Do you have a contract? Seems you need to. Address the hours she is expected to "work" and the conditions of her "work time": not "on" any substances, completes tasks in a timely manner, respectful of her clients and their home... She is an adult and not liable to anyone for her "off duty" behavior. The only problems may be if she has obnoxious behavior "off duty" and she lives in the home. It might be a good idea to have her leave a notes of her expected return home in an agreed upon location if she will be late in getting "home".

I guess that I missed something here. I don't see anything in the OP question about car stealing and men being snuck into the house. Must have been a response OP gave to a questioner or commentor?
Does anyone notice how many questions we get on the forum and the OP never shows up again. It has led me to stop going through all the answers and responses. Makes me kind of wonder.
Am wondering now, what the choice was by the OP and was the result was. What if any actions were chosen, and what the outcome of that was.

Have you thought of having her take UA tests?

Sneaking a guy in the house and taking the car should be huge red flags. BOLO for other inappropriate behavior.

As long as she does the job she was hired for, what she does in her private OFF time is HER BUSINESS. As long as she is on the job and doing it properly when she is supposed to be working, fine. If this doesn't suit you, I'd look for someone else but when people are "off", their time and what they do is their private right. I'd be furious if someone tried to control what I do in my off time.

Asking this question is a "RED" flag and your un-comfortable.
Time to re-hire.... by the way put a freeze on your love ones credit accounts, bank accounts and anyone else who lives in your house.

Upon hiring a live in it is discussed what times she has off.

If it was agreed that she has her weekends off then, what time she comes un is really her business.

If she is disturbing you when she comes in at that time, let her know that and if she has the weekend off, tell her to either cone back at a certain time or stay gone til a better time like 8 or 9 in the morning or ask her if she has the whole weekend off, tell her to leave Friday at 5 or 6 and not return til Sunday 5 or 6 PM.

It is whatever was agreed upon when she was hired.

Some live ins only get 1 day off a week and some only get a weekend a month off.