She's lurking. Ball pythons are ambush hunters so will often use this position to strike prey from cover. Is it her normal time to eat as far as date and time (as in does she normally eat during the daylight hours or at night). Ball pythons are nocturnal so you may find evening feeds work better for some of them. Is this the same size rat, presented in the same way she's used to? Ball pythons are very funny snakes about habits they are used to and tend to be very prey specific. They want their dinner, in the way they are used to getting it, when they are used to getting it. No wonder they are called "royal pythons" LOL.