Poor little J, how far you've fallen. Looks like the Upper East side has managed to swallow you whole, and leave nothing behind. Lets take a look at where she started and where she ended.
J season 1
We start off in J's 9th grade year at Constance High, she dreamed of being in the world of the Elite, she may have been the runt of the group but, she was one of them. J challenged Blair, she showed she could keep up with her, and surpass her. That was her 1st mistake. We all rooted for Jenny, she showed you can win with morality, she was our light of hope in the dark dark world that is the Upper East Side.
J season 2
After Jenny's fascination with the Upper East dimmed she decided to bet on herself and her skills. Jenny set her sights toward fashion and nothing was going to get in her way. She dropped out, rebelled, moved out, and basically went from 14 to 40.
J season 3
Watch out! lil J goes goth! J finally became Queen B of Constance and it turned her upside down. Lying to her parents, bullying her stepbrother, she became exactly what she feared. She tried to rule with freedom to all after being buried by former queen Blair Waldorf, but the minions wouldn't take that lightly, she tried to fake it at school and stay the same person, but ultimately the Upper East side won the battle.
J season 4
oh J, by this time everyone was glad to get rid of you. The season of Jenny's departure. TBH when Blair banished her and she moved to her moms house I was relieved. She just took it to far. Sold drugs, bullied her brother, tried to steal Serena's boyfriend, tried to break her parents up, lost her virginity to Chuck Bass on the night of his proposal to Blair! She turned into one of them, and soon Dan followed. Looks like the Upper East Side was to strong. This was one of the last times Jenny was seen she appeared for a few more episodes but even when she did return she lost it. The Jenny Humphrey speculation is that her character changed based on the actress who played her (Taylor Momsen) acted. Taylor began wearing dark clothes and makeup, acting out, and they made her character reflect that drastic change.