We never really get to know Jenny Garp, but as her name implies, she's the perfect mix between her grandmother and her father.
Like her famous grandmother, Jenny Garp commits herself to nursing and feminism. In fact, she even talks highly of her grandma, despite never getting to know her. Young Jenny remains inspired by old Jenny's feminist ideology, her commitment to nursing, and her headstrong nature. Plus, she shares the elder Jenny's poor writing ability.
She isn't just like her gram, though, and like her dad, Garp, she's funny and sarcastic. She makes light of the fact that she is a "doctor who sees only terminal cases" (19.305), for instance, which reveals a drastically different approach to medicine than Jenny Fields possesses, since she seems to get more out of the actual comforting of people than the medical part.
Interestingly, Jenny Garp doesn't get to know her father very well, either. She's born late in the game, and he dies before too long. In a way, though, it's fitting that Jenny's the last Garp we see alive: She has the best of her family, but none of the baggage.