The good news: you’re not technically liable for taxes if it’s not an obligation specified in the tax code. Simply holding money for her should not result in your owing taxes. (Study the tax code at every level of obligation: federal, state, county/village/town, estate).
The bad news: the IRS (and State Depts. of Taxation & Finance) is (are) the only branch(es) of government that traditionally operate with a guilty-until-proven-innocent paradigm.
The reason I have an accountant to answer such questions is that what you are entitled to do does not necessarily suggest what is in your best interest to so do.
So first ask if the potential triggers and red flag nature of doing this outweigh the trouble of doing it a different way. In addition to asking an accountant, you can try to ask the bank. They may not want to offer advice, but some may be implicit in their policies.
And if you decide they don’t and proceed, keep careful records and exchange copies of each others records and hang on tight. We hope you won’t ever need to use them.