Anyone who's met our cats know that they have about a zillion nicknames that change all the time. Even Dave gets nicknames from me, but I try not to embarrass him by using them in front of anyone. It should come as no surprise that Fiona has not been immune to my predilection for nicknames.
Some stick, some don't, but here are a few so far: sweet pea, sweetness, sweets, princess (I know, I know -- I said I was going to stay away from all that princess stuff but I can't help it), squirrel, squirrel-monkey, squirrlsey, squirrelness, squirell baby and Fi.
Just don't call her FiFi. That is a poodle name.