Having PII in Google Analytics is a big no no, it violates their terms of service and can cause you to have to remove all your analytics data - not fun.
The good news is, most 'standard' Drupal sites using most 'standard' GA implementations avoid sending any PII with one exception - and that is the user password reset page.
The problem occurs when a user attempts to login but enters and incorrect password. They are then presented with a message saying "Unrecognised username or password. Have you forgotten your password?". The "forgotten your password" bit is a link to...