Can I use my email address to file a 2025 tax return for my cousin? she has had a stroke

[xmasbaby0]

You can use the same email address for up to five online accounts if you are using online software.   But each account needs its own username; when you use online software you pay for each federal and each state return.   And...you would not be filing a 2025 tax return.  Users are preparing and filing 2024 tax returns.   No one will file a 2025 tax return until next year in 2026, when tax year 2025 is over.

When you use online TurboTax software 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, the second one overwrites the first return and it is lost forever.  

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...