She is nothing more than a teenage girl stereotype who spends much of her time talking on the phone to school friends about their dates and her own activities.
She is very dumb, as she always thinks that Tom is bothering the baby, completely unaware he's either chasing Jerry or the two are putting the baby back on the crib or carriage. She hits him on the head with a broom afterwards and tell her friend on the phone about the "mean cat" before resuming their chat.
She is a big jerk to Tom, mostly because she keeps hitting him with a broom even when it's undeserved.
She also hits Tom even when he and Jerry are trying to keep the baby safe.
She gives no gratitude to Tom whatsoever whenever the latter helps look out for the baby she neglects while she spends hours on the phone and often beats him over the head with whatever object is handy.
When Tom and Jerry both do their best to bring the baby back home and put him in bed, Jeannie claims that the two were bothering the baby. However, it looked like they were stealing the baby, and wouldn't you mistake someone for stealing a baby at times?
She is not a good babysitter at all, because while the baby's parents are out, she regularly blabs on the telephone rather than doing her job, However, in Tot Watchers, she is far more neglectful towards the baby than she was in Busy Buddies, having made no attempt to look after the baby at all unlike the previous short.
On that topic, in both shorts she appears in, there's at least one occasion where the baby unknowingly crawls all over her from head to toe as she blabs on the telephone, and she doesn't even notice about it, let alone doesn't care.
She has never exposed as being a terrible babysitter, nor has she ever been punished or even called out for her neglectful behavior to the baby, making her a karma houdini.
In fact, in the ending of Busy Buddies, when Joan asks her about how was it babysitting the baby, she lies to her claiming that the baby "was an angel" and is "no trouble at all" which turns out to be false once the baby winks in front of the camera, implying that the baby, contrary to what Jeannie claims, caused a lot of trouble to both Tom and Jerry who were babysitting him the whole time, while Jeannie did answered that only because she barely even tried babysitting the baby throughout the entire short.
She rarely babysits, so the baby is safe most of the time, and Tom and Jerry don't have to deal with her that much.
Despite her sub-standard babysitting skills, she is actually very kind and friendly and has many friends in high school.
Her design is decent.
To be fair, she wasn't aware that Tom and Jerry were just trying to protect the baby.
She became one of the unfavorable characters in the franchise by fans, alongside Tom's notorious owner from the infamous Gene Deitch-era and Nancy from Baby Puss, although, as mentioned above, she's nowhere near as abusive as the other two.