How can I show her?

We went out the other night, her girlfriend (Kate) called with a suicide threat and made her cry all night because she is 'insecure' and needed more 'reassurance'. I'm aware the girlfriend is probably jealous of me even thought my best friend (Cat) says that she is not.

So Cat has always got in to manipulative relationships but the other day I actually spoke to her and said that Kate treats her badly, she cried on the entire night out and we went home.

Honestly? I just want her to see her worth and make her understand that she will always have the pick of the bunch. She is worried because her family love Kate. Do you guys have any advice?