How should we start the rp?

I'm not sure. Your idea is enemy becoming an ally, right? How would that work?

Maybe they pick up on irregularities on official Zootopia data?

And my character automatically believes it's a hacker, and he knows yours is one, but doesn't know where she is?

Sure!

What kind of irregularities do they notice?

Stuff such as someone being able to get through a firewall. Or maybe its private data and they can see it being viewed by a non permitted address?

And maybe things start happening to those whose info has been compromised?

Sure! My idea was that she would try to find data as she is convinced someone is hiding something

She should send a secret message to my character at some point proposing to work together.