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.
Any time you change the title on your home (unless you are taking a spouse off the property or transferring to a Trust), most counties are going to subject you to transfer tax and reassess your property.
Removing someone from the deed, as well, unless that person is married to you or deceased.
It may require lender approval add a person to title.
Person could be obligated to taxes, and if you were sale home release of both parties sign listing agreement, and closing documents transfer title to new buyer
I am a Realtor & an Attorney licensed only in OH, so my comments are my personal opinions. You need to contact an Attorney who handles residential real estate matters. In general, you can add someone to the title for your home during the purchase process. You are the one who is buying the home, that person will not be on the promissory note or the mortgage, but you can decide whom you want to have title of the home by telling the title company to have the deed prepared in a certain way (this is one of the items you discuss with your attorney). Contact an Attorney for adding someone to the deed after the purchase process. You will want to discuss what type of ownership you want to convey. There are a number of types of deeds & rights to possession of your property, that's definitely why you need an attorney. Also, talking someone into giving back his/her interest in the property by signing a Quit Claim Deed is not that simple if they don't want to give away their interest in the property. There are gift tax issues if the home is worth a significant amount & you have a lot of equity in the home. Some of the answers you received earlier, mention trusts. Again, this an Attorney would prepare (& there are different types of trusts for different purposes). In summary, this is not the forum to obtain the answers you need; you definitely need an Attorney.
Ask a lawyer. I am sure I got some of the details a bit off. The concept is strange and had to be designed by a lawyer who can think sideways upside down and around a corner.