I think I’ll tell her a mates mate is a lawyer and says they can be added together n she could get 5years. That should scare her off it.
Can't hurt.
There's a whole bunch of things you can try, but you probably want to make sure before trying any of this. Some depend on your living arrangements and some are a bit extreme, so it depends on how far you're willing to go...
- tell her there'll be consequences for your relationship if it continues, especially if the Police show up with a search warrant.
- threaten to dob her in yourself if she doesn't stop.
- don't let her shop with your cards.
- don't let her shop alone.
- check all receipts against the items bought.
If nothing else works and you're willing to get others involved...
- if she comes home with something she hasn't paid for, take her back to the store and make her explain herself.
- speak to the store manager and ask them to watch her at the checkouts in a "very obvious way" - she should quickly realise that "they're onto her" and that might be enough.
- go see the Police and ask them to come and have a chat to her. They do that kind of thing all the time (especially with minors), so they will certainly know how to put a real scare into her. The Police can actually be very good at dealing with these types of situations.
Be creative and try whatever you think will work. But keep in mind that it might not work, in which case if you really want to stop this behaviour, you might have to act and obviously, there could be consequences if you go down that path - both for her and for your relationship.
If nothing works and she won't stop, then at the end of the day, getting caught might be the best thing for everyone - her, you and the store.