How do we find a sitter listed before now does not come up in search?

Call Customer Support [Edit: Rover’s contact options have changed. Visit the Rover Help Center at https://support.rover.com/ to find the phone number, help articles, or chat with the team] they will assist you

In addition to Walt's advice, you can always find sitters you've previously used by going to your Inbox/Past Stays, where you should see the messages from those stays.

Definitely call customer service. But if she's not showing up in past sittings, she's left this site.