Yes - You can purchase and install the CD/Download version of TurboTax by clicking this link:  TurboTax CD/Download [If you haven't printed or filed your online return yet, you will not have paid for it.]  

You can download your online return to your computer by following these steps:

1. While in your return, click on Tax Tools > Tools (in the black bar at the side of your screen). 
2. Under Other helpful links click on Save your 2020 return to your computer.
3. Your online return will be found in the Downloads folder on your computer.
4. To open the return in TurboTax desktop edition, click on the Find a Tax File link on the opening screen and then navigate to the Downloads folder. 

I have already filed my return using Premier online.  Can I now get credit   for / trade in the online version for the download version so that I may file my 94 year old mother in law's return(s)?

If you paid for an online return call in and ask if they can switch you to the Desktop program.  They might be nice and give you the download.

Contact Customer Service
5am-9pm Pacific Time
7 days a week
https://support.turbotax.intuit.com/contact/

What is the Turbo Tax phone number
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632

You can probably prepare MIL's return on TT Free online.