Full isolated browser

Hi,

I have a problem...
My mother (an old woman) use hers computer to check email, navigate internet, find information.
About every 3 moths I have to reformat the computer for viruses, unwanted programs, crashed file that slow down the machine.

I would portabilize a browser (I prefer Ungoogled Chromium) in FULL ISOLATED sandbox.
The problem is the conflict with the sandbox builted in into Chrome.

Have you any ideas how to perform this goal?

Thanks

P.S. I would create a PORTABLE (not only isolated like in sandboxie, but full portable like Turbo Studio, Evalaze, VMWare) browser with accounts registered and in automatic delete data session at the browser exit.