How do I file a tax return for my elderly mother via Turbo Tax? Do I need to set up a separate account for her?

Yes, you can use TurboTax to file for your mother. You need to create another TurboTax account.

Please read this TurboTax FAQ:

https://ttlc.intuit.com/replies/3288574

Yes, each tax return requires a separate account with a separate username and password, but you can use the same email address for all of them. Never start another return by going back and overwriting everything in the return you just filed. This will replace your info, which means you won't be able to retrieve your return later.