I think that Jenny ended it in Paris because of two things. One being her career. Second I think Jenny has some trust issues and didn't want to put her heart on the line. She loved Gibbs, of that in mind there is no doubt. She just couldn't risk relying on someone and having them hurt her again.
i think she ended it because of her job but then once she saw gibbs again she realized what a huge mistake she made and im sure that she regretted it everyday for the rest of her life.
