Yes you can still file jointly and file for the tax credit as long as you qualify under the tax credit guidelines. Meaning no homeownership for either of you in the last 3 years. Im confused as to why you would have to "go back the next day" to have her put on the deed? This is a common thing to do AT closing with married couples. One on the mortgage but both on the deed. But its done on the inital closing.

Hi Dahlia,
Since this is very new, I suggest that you talk to your accountant if this is a great concern to you. Good luck on your new house