I have conundrum.  My wife is the anti-tech*.  Somehow she has two Google accounts.  One, with her Yahoo user name, we have the password for and her phone is attached to it, etc.
The other one, with her Gmail user name, is active (Google Fi account, she gets her Gmail, etc.) but we don't have the password.  Account recovery takes her (same) phone number as valid, but when account recovery sends a notification to her phone number, nothing happens.  No notification.  Once it sent a text but refused to accept the provided verification number.

* She has no idea how this happened.  This is a person for whom fingerprint sensors don't work, won't use a password manager, hass dozens of passwords written in tiny letters and scribbled changes, etc.

Check the password functions in the browsers on her computer and phone. While she's might not use them, they may have captured the passwords anyway.

Sounds like she is using a second messaging app. Check the native app to the phone for messages.

Did it.  There's a Google entry with no user name but the password is an old one & doesn't work .

Google sends notifications (system notifications).  Those don't come through from account recovery to her phone for that user name at all

As texts go she's using the native Google text app.