Cybercriminal with email id hacking gmail account

The domain investor does not use gmail, only for review purposes a gmail account was required.
When she logged in,she found that some cybercriminal with email id had hacked her account and is misusing it
This is a copy of a security alert sent to is the recovery email for this account. If you don’t recognize this account, disconnect it.
Account recovered successfully
Welcome back to your account
If you suspect you were locked out of your account because of changes made by someone else, you should review & protect your account.

Anyone who knows the identity of the hacker,please contact at