Cassy was a fat whore who was paid by Dr. Malarious to give him orgasms when Lawr-asse wasn't there. Her weight is about 3 tons so we don't know how the bed didn't break when she sat on it. What a fatass. She is also very dumb. Her IQ is about -69. 

Ratchet & Clank wiki
For those without comedic tastes, the so-called experts at the Ratchet & Clank wiki have an article about Cassiopeia.