Sorry for your loss. for security purpose, I doubt that Turbotax will provide info to access her account. you can't use your account because they are only good for 1 taxpayer. do a second return in the same account and the first return will be wiped out and unretrievable.
you can try customer support to see if they'll help but since you are using the free edition support isn't provided without upgrading or paying a fee
as executor you can request a copy of her last year's return from the IRS
- Download and complete IRS Form 4506 (Request for Copy of Tax Return)
- https://www.irs.gov/pub/irs-pdf/f4506.pdf
- Prove you are the executor by including a copy of your court-approved "Letters Testamentary", or if there have been no court proceedings, include IRS Form 56 (Notice Concerning Fiduciary Relationship)
- Also include a death certificate, and the required IRS copying fee
- Mail everything, and expect a response within "a few" weeks
