I would do 10-15 minutes 2-3 times a week MAX. I have successfully tamed the 3 nippy/hissy babies with even less handling than that. The key is to make sure the handling sessions are positive. Reduce stress while she's out as much as possible, and try to keep her isolated from anyone else in the house until she calms down a bit. If she gets nippy, do not put her up until she stops biting, otherwise she'll learn that will get her left alone. When bringing her out, let her know you're there but don't take your time getting her out, the longer you take the more she'll get worked up. They're generally but not always better once they're out. It might help to put something that smells like you near her enclosure. I hesitate to put hazardous stuff actually inside my snakes' enclosures, but she should smell it just fine from right next to her enclosure.

I would also make sure you have plenty of cover in her enclosure, as that's what really helped my youngest male boa. I added just one or two more hides and he calmed right down. Took a few months after that to get him to stop huffing when I went to pick him up but the nips virtually stopped and he wasn't defensive once out anymore.

Also, do be prepared for this to take time. Sometimes baby snakes just stay defensive until they get some size on, which could take a year or two. Refrain from overfeeding to calm her down (yes this is something I see people do and recommend), as all that will be doing is damaging her body and lowering her life expectancy.