Is there a better, safer, mail client to use in her case? Getting them all in one app would be her goal to save time, and still have a way to tell from which account each message comes from. And also scheduling working more seamlessly than it does.
Outlook for Mac 2019 is pretty stable and does all that quite well. For Gmail, I mostly use Mailplane (https://mailplaneapp.com) which I have used forever and it has been pretty solid for me always.