Bullied by barn manager, really bothering me

I love my barn manager; however, she nickels and dimes me to death. Tonight she said I owed her $10.00 for deworming for Nov.. She wormed last month....late as I paid her in October for it. Then she said, "well, I'm worming late this month". I also gave her $300.00 worth of free inhalers for her and her partner (free from my doc dad). I was being nice because they were both sick. I don't HAVE money, but I'd rather her just jack up the board again than give me ShiiT.

This sort of thing happens frequently. She also acts pissy when I don't help her with anything and she doesn't give me a break on board or turn ins EVER. I turn her horses in and feed them frequently.
She acts like my best friend one moment; although, if a new boarder comes in, she treats me like I'm no longer her friend?????? Oh and every new boarder that comes in, suddenly becomes "barn manager" for a month or so, until she decides they are inadequate. Including me.....

My boyfriend and I confronted her about the charge this evening and she just acted really rude about it. This is the same woman who let me sleep on her couch and comforted me when I had to put my dog to sleep last year.

Also, the same woman that dewormed my horse on an empty stomach during a cold spell and he colicked last December......did she take any of that responsibility NO!
I can't afford move and my horse really likes the herd.

What can I do? My boyfriend says, just get a receipt for everything.....but it's more than that. I have tried to have a heart to heart, but she gets defensive etc. etc.