She didn't steal your laptop. She asked to borrow it and you haven't asked for it back.

Besides, she pays for the place you live in with her own money and lets you use it. It seems a bit ungrateful to be immediately resentful to the point where you label this as her "stealing" from you once the situation is turned around on you. You are 24 now. You don't have a parent/child relationship where it is her responsibility to take care of you. You are equals as adults.

You would be justified in demanding your laptop back, since you paid for it yourself. But she would also be justified in demanding that you pay rent or get out, since she paid for her residence herself. So keep that in mind when making your decision on what to do.

You don't even have to take it back from her completely if you don't want to. Just say "Hey I want to use my laptop for a bit to do some programming" or whatever and just let her use it whenever you aren't using it. It doesn't have to be in sole possession of one person where the other isn't allowed to touch it. You can let her on the main computer if you want to use the laptop.