Why is Gmail moving all new emails to the trash?

This kind of issue often stems from clicking on suspicious links. What likely happened is that your wife fell victim to a phishing attack; a bad link could lead to a fake login page where attackers got her credentials and set up that rule to keep her from noticing any odd activity, like password change notifications.

Exactly! If they can hijack a session cookie, simply changing the password won't help. It's best to log out of all devices and reset her password completely. Also, enabling multi-factor authentication (MFA) would add an extra layer of security.

This strongly suggests the account may be compromised. I’d recommend checking all devices, logging out everywhere, and changing the password immediately to prevent further issues.

Another possibility is if there were auto-forwarding and delete settings active in the account. That could cause emails to get forwarded to another email address and then deleted from her inbox, giving the appearance that they're going straight to trash.