Thanks for the details, when was the last time your wife successfully signed in to the live.fr account?
To recover access, Microsoft only supports two steps: fill out the Account Recovery Form and provide as much accurate info as possible about her account, like older passwords, email subjects, and services used, because support agents cannot reset an account if the current phone or backup email are unavailable.
If the recovery info entered is insufficient, you must retry with more details until the system verifies ownership.