All I can think of is that when you went to "spot clean" her enclosure, you didn't really identify yourself & maybe she was sleeping? The adult bull snakes I've kept never
bit me either & seemed very capable of telling me from prey (I typically give them my scent first). If she has taken a dislike to you reaching in (within strike range) you
can just put something in the way (like a piece of cardboard) to block her from seeing your "intrusion". I often do that with my large Florida rat snakes if they are in their
hides & I want to spot clean...I just block the door-way (with a ping-pong paddle) so they don't get "excited" & fly out after the motion (me), hoping it's a snack...