can I deduct mortgage interest if I am not on the mortgae but am on the title/ deed

[NiceGuy123]

What is the name of your state? Minnesota
I moved in with my gilrfriend. She filed a quit claim to put me on the title.
I am not on the mortgage. She made less than $30000 last year, so she is in the 15% bracket. I am in the 25% bracket. Through the last year, I have had to come up with more money for her than all the mortgage payments. I was thinking I could recover some of that by claiming that I paid the mortgage every month. Between federal and state, I would get about $3200 back. Where she would only get about $2000. And with the standard deduction she already will get $1000. So we could pull $4200 back from the government instead of just $2000.

Is proof that I paid the mortgage each month required, or can she let me claim it by giving me the document showing the interest paid?

I do live there if that matters.

Would we need an agreement that the money I spent was to cover the mortgage?

Can this be verbal? Or must it be written? If written, does it need to be notarized?