It looks like you are posting from desktop software. Are you using software that you installed/downloaded to your own computer? If so, there is no need for you to use passwords or user ID's for your mother's tax return. You just prepare her return and saye it on your own hard drive.
I buy the program every year and down load to computer but if I can use my email account for her tax return then I will because she doesn't have a computer or internet service to even justify email account
Just use your own email address. I do that with returns I file for other family members. That way I can keep track of what is happening with them in regard to seeing if they are accepted, etc.
You can use your email account to set up another username and password for your mother's return.
You might want to switch to the TurboTax CD/Download software to save money
If you still want to start another return in TurboTax Online, here’s what to do:
Can I file my taxes without an email or can I use my girlfriends email
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.