Not much of Jessie's past is known(i dont know it anyway). But I do know that Jessie more or less
grew up with James ever since they met in the Pokemon Tech school. Jessie can be very bossy towards James alot, but I can tell Jessie has feelings for him, its the way they act toward one another. And she is just trying to help the team out(since James is so lazy^^)
Her attitude is also on her looks sometimes, than anything else. Other than the bossing poor James around part I think Jessie is a rather tough cool girl^^.
Go back to Team Rocket's Pokemon Warehouse