I personally think Jennifer got ruined when Jack returned and she had absolutely zero sympathy for what he had survived. Even in the cabin, when he had his terrible panic attack and she told him she loved him, assuming he could not hear her, Jen Jen got mad at him for not speaking up !
Well, Jenny, Jack had other things on his mind. But since the world revolves around Jennifer, she cannot get that.
For a while now, Jennifer has been throwing accusations and passing judgments on others, all the while not having all the facts. She did it with Jack, when she accused him of following her around on Halloween (I still wish we would know who the Halloween figure was... though I suspect the writers don't even know themselves, thus they dropped the whole thing). Jennifer didn't even bother to call JJ to confirm that Jack had indeed been in London visiting with him. And she did it to Daniel, by accusing him of having an affair with Theresa (to hurt HER), and now, she accuses Daniel of having a thing with Kristen.
Jennifer is also a stalker who doesn't know when to stop harassing people. When Jack died saving their daughter, Jennifer barely shed a tear, before she proceeded to harass a very pregnant Nicole. And not once did Jennifer take part of the blame for the fiasco that followed. Nope, she was too busy shining her crown, as were all the good Salem citizens.
She's also a very controlling woman. She keeps following Daniel around, barging in on him, deciding what's best for him, what he should think, what he should do, how he should do it (the hand tremor thing was horrible as she never once stopped to take Daniel's wishes and worries into consideration) and when Daniel doesn't do what she wants, she does it herself, thus she told Eric about Nicole's lies.
Seriously, if Jennifer were a man, she would be perceived as a violent abuser. But since she's Jennifer Horton, I guess she can do as she pleases.
I just wish we could get rid of this horrible character that is now Jennifer, for good.