Certainly under some stress, may be piggie version of menopause or heat. Biting is likely doing something that scares her or really annoys her. Maybe spend more time with her just letting her do her thing. Chasing, grabbing or picking them up, they don't like. Forcing them against their will to do or not do something they want or don't doesn't work.
Less stress when they have freedom to come and go as they choose and have places to hide.
They always need their hay to chew, their teeth get too long, that can be problematic.
My trio were rescues, one never got past shy, but would still come for a treat or cuddle next to me under a shirt nibbling hay. Takes time and patience with these little animals.