[Kagen4o4]

well as someone only a few years out of their teens. i must say i use to love stealing (granted i never did from friends and family). but there is a certain excitement to it that you only get from taking something that you could get caught for.
my suggestion, talk to her about it, dont get angry with her and try and control her. that will make things worse. let her know that its out of your control and you cant stop her from doing it, tell her there will be consequences if she gets caught that go beyond any punishment you could give.
tell her to ask her friends whether they care if she steals from them. she'll want to talk to them about what you said to her, but she wont be able to because it would mean she is addmitting to stealing from them. and she'll realise that since she cant talk about it that maybe she shouldnt be doing it.

in most cases its just a phase because they realise how easy it is to pick something up and walk out with it. once they realise that someone might be watching them, they should back off a bit.

if it does go beyond this, any advice i could give would just be guessing