I'd like to give some context:
I'm a hairstylist. Right now I'm working at a commission salon, which means I receive 50% of every service I do plus tip. I'm newly licensed, so I have the least amount of clients. My boss totally takes advantage of me. Making me deep clean her salon all the time, help her daughter with her clients (even though her daughter doesn't pay anything to her or me), and on top of that barely advertises me on our social media. This isn't the main thing I'm upset about, though.
A long time ago she told us we would need to pay for the products we use when we do our own hair, which is fair. It was never really set in stone because she never told us if we should check out like a normal appt. or if we would just pay her. Well I had my hair done once this year, and the girl who did it completely fucked it up and I had to have it fixed 3 times. (My manager even said it was messed up. She literally fried my hair.) Well I have now discovered on my pay stub she has charged me $80 for all of this, even though she KNOWS my coworker fucked up. I also know she can't just take money out of my paycheck without me signing anything (there has been no employee handbook given to me to sign either). Also, she's been taking advances out of my check even though I have never once asked her for one.
How do I go about confronting her? I'm a pushover so I need some help. I don't want to be aggressive but I do want to be assertive.