I basically made $3k off my friend
How did you make that kind of money from your friend?
I've been selling her old accessories on eBay behind her back
It's extremely wrong to sell someone else's things, and betraying their trust is even worse than stealing. You could get in a lot of trouble, and your friend will probably not trust you ever again if you don't tell her. If you tell your friend before it's too late, she might forgive you and should just ask you to replace the accessories.
But I feel like there's nothing wrong with what I'm doing, i was just trying to make some funds with stuff she didn't want. I'll just talk to her about it.
Well, I don't really understand your friend's situation, so maybe you're right.  If she tends to discard or abandon old accessories that still have value, then maybe she wouldn't mind, but you really should have talked to her about it first, and asked if you could sell them.  It is still betraying her trust to take her possessions, regardless of how she treats them.