She's also a 14 year old girl, which is not the easiest age. She's also dealing with something, her sexuality, which is hard for someone that age even now, but much harder in the 90s when it was less acceptable, or at least more of a novelty.
I don't hate Izzy, but she is difficult. While I don't *like* a lot of the characters in this show, I think that is the point.
FYI...I moved the answer to this to the Book Questions thread to avoid spoilers.