Almost every ball python will grow out of nippy baby behavior. Your girl sounds exactly like how my Minnie acted, and now she lets first time snake holders handle her without even a hiss. Some desensitize to the threat of human contact more quickly than others. While she's still showing a lot of fear/aggression, don't bring her close to your face. They may not be very bright but they seem to know what might happen when they're brought too close to a mouth.
With quarrantine, do the best that you can. Best would be different rooms on different levels of your house. Best that you can might be keeping their cages on opposites of the room with their own husbandry equipment and washing up good and changing clothes between handling. With me what worked out easiest was to do the established snakes when I first got up and the "cootie cage" later in the day.
Opinion varies as to how long you need to quarrantine. Read up on it and use your judgement.