Please, please check with a lawyer first.
Adding a person is cheap. I don't know, maybe $150-$200. Maybe less.
In most jurisdictions, there wouldn't be a transfer tax. I don't know about Vacaville. A lawyer or settlement company could tell you.
Tax consequences? Yes, possibly. It really doesn't matter if she pays you for it. There should be "consideration" which could be only $1, or maybe $10. Often, with intrafamily transfers, no money is exchanged; the "consideration" is termed "love and affection."
Other consequences? You'd be violating the lender's due on sale clause. You'd be transferring equitable interest in the property to another person without prior approval of the lender. And, technically, the lender could call the loan due and payable. Bluntly: The lender could foreclose. That's unlikely, but possible.
Removing someone from the deed? Impossible (or nearly impossible). Once someone's on the deed, they're an owner. They'd have to relinquish their right, perhaps with a quit claim deed. If they chose not to, it'd be nearly impossible to force them.
Please, please consult with a lawyer (and possibly an accountant) before you do anything.