You can use your GF's email address, but you need your own account and user ID. If you use her account and user ID you will overwrite her tax return and it will be lost forever. But why do you not have your own email? It is so easy to set up a free gmail account. Have you tried?
Using an account that belongs to someone else in any way sets you up for problems for someday if she is not your GF any more.
When you use Online TurboTax, you get one return per fee. Each return needs its own account and user ID. If you use the same account and user ID for a second return, you overwrite the first one and lose it forever.
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
