Wow wow wowww, I admire you for being so cool about the whole thing, really. You don't sound immature to me at all and certainly not ungrateful. What a sad shame! She sounds crazy to me too. It's sad that her personality is so disagreeable because the arrangement you have seems ideal other than that--so I totally understand you not wanting to leave. You shouldn't have to put up with that kind of abuse though--yes, there may be worse forms of abuse out there, but that doesn't mean this kind can't do its share of damage. Often it's the minor but persistent forms of abuse that can do the most damage, because it slowly erodes you without your hardly noticing.
I also TOTALLY understand how you feel about the money thing. I think a lot of us are feeling that kind of pain. I'm also trying to find a work<=>ride etc. situation, but my location makes that a bit difficult at this point. However, I'm SURE there are people willing to do that kind of arrangement out there--and chances are they're far nicer than this person. Just get out of there.
If you have a horse already, then you'll be OK I think while you search for a new trainer. You can learn a lot from your horse without a trainer even, from what I understand, and it may prove to be an interesting period of growth for you while you're sorting things out on the other end.
Good luck, and I hope things improve fast!