[Aliantha]

Maybe if she's the manager you can set up a meeting to discuss the money missing from the till and impliment some new procedures - possibly only one cashier - although I know that's tough in a hair salon, but just let her know that you're not prepared to put up with it any longer, and the person will be caught and dismissed immediately.

Maybe she's got some financial issue which is her reason for stealing. I know that's not your concern from a professional standpoint, but good staff are hard to find. Perhaps if you have that convo with her, she might own up and let you help her, if you feel so inclined.