A four-year old BP is pretty much an adult...it's not rare for them to eat less often*, or go on a fast if they've been routinely over-eating. *I'd feed every 2-3 weeks
as bcr229 posted above. And for what it's worth, I also don't think most snakes make good classroom pets, & especially not the more sensitive ones like BPs -that
need higher heat & humidity levels, & tend to be shy feeders. A better choice might have been a corn or other type of rat or gopher/bull snake. BPs are also more
nocturnal when it comes to feeding habits, which puts them at odds with a classroom. You may be seeing the cumulative effects of stress, fear, lack of sleep, etc.
Please keep in mind that long term stress can predispose animals & humans alike to illness when it continues. This might be a hint...
I assume you know that snakes typically refuse food for a while when in a shed cycle too...have you checked her eyes for 'blue'? (in dark room w/ penlight)