gmail invisible in apple mail

Hi again!

On behalf of my wife:

On a very new MacBook air, 3 email-accounts have been correctly configured:

a mywifesname@icloud.com

a generic IMAP-account

a gmail-account (which is required as she uses an androphone)

Now, the gmail-account is not available anymore: It is simply NOT in the mail-accounts list (in mail.app's side-bar.

The account is (was) configured, worked, and its checkbox (activate account) is on.

It is present on the phone as well as on her ipad...

Should it be removed from the mac and reinstalled, or is there a simple solution, like ticking a checkbox somewhere?

thank you (again)!