I can't confirm anything about this bio, because, well let's face it there isn't that much info based around her and Butch, so sorry if this isn't the most detailed or whatever, but I want to come as close as I can to the true about her age etc.

Name: Cassidy
Age: 17
Pokemon: A Raticate, unfortunately not a very powerful Raticate.
Height:Well judging for the height of Ash (which you would think around 4'11 to 5ft), and Ash' head comes up to Jessie's chest, thats about 1ft, and then Cassidy realisticly speaking would be about 2.5inches taller the Jess, thus making her around 5'9 to 6ft tall.
Weight: Cassidy and Jessie, both being taller and having a larger breast size for the average 17 year old, would most likely be a little heavier than one.
Maybe around 125lbs to 135lbs.
Goals: Just like J&J, Butch and Cassidy have missions to complete, etc. But, I think from watching the first Ep. with B&C in it, that Giovanni trusts them a lot more than J&J.
Cassidy must have some sort of goals in her career, maybe even to get out of it.(of course something tells me she'd never let Jessie win like that.)
One of them may be to beat Jessie, or complete more missions than her.
To tell you the truth I have no idea.
Friends:Wow, this is an easy one. I think that Butch is her best friend. He doesn't seem like he says much on his own, but when him and Cassidy are talkin alone about something, he'll talk because he knows that Cassidy isn't perfect, but will respect his opinions and dreams. It looks like the two need each other. They may even be something more....
.......but......I'll let you decide that.
Foes: Cassidy seems to have been friends with Jessie as a child, but something happened and now they can't stand each other. Also I would think Todd and Ash(and co.) would be on her "shit list".
The Hair: We've all thought of it at one point in time, how does Cass get that hair? Well....my guess is that her hair was always spiky as a child, but as an "adult" she decided to put her hair in ponytail thingies. Just like Jessie did, she was a child, her hair was always curvy, and she just put it up.
Do I think Cass always has her hair in the tails?
No. Do you or your girlfriend or your girl friend always have your hair up or down? No.
Though maybe I'm wrong.