You say "all" like it's more than just email but then only mention Google. So are "all" of these Gmail accounts?
When you upgraded did you pass your old device down to her? Did you ever use her device to access your account or use Find My Device?
Do you talk in your sleep?
You also seem alarmed. Is this because you would not like her to have this access or do you just want to know how it was possible?
If we're talking "only" about Gmail accounts, (email, Drive, Photos, Voice, etc.) and you wish to restrict access, on the same security page where you were able to see active devices you can revoke selected devices or all devices and close any active sessions. Then to prevent future access change your password and possibly turn on 2-Step. Once you've revoked permission, closed active sessions and changed the password even devices that have a saved password or could autofill the password will require a fresh log-in. By adding 2-Step access would also require possession and access to your personal device.