She might have recently drank water too. Keep an eye on her- whistling CAN be a sign of an RI (respiratory infection), along with clicking & crackling noises, open-mouth breathing, bubbles in or around the mouth, & slimy inside the mouth. If the whistling isn't temporary & especially if you're seeing other signs too, get your snake seen by a herp-oriented vet. Too much mucus can choke a snake, as they aren't really designed to cough effectively- they can also aspirate. Usually a snake with an RI won't want to eat, also. Double-check the temperatures- if it's not already at the upper end for safety, try raising by a few (2-3) degrees- that may help a mild case recover. And remember to quarantine the sick snake from others if you have any.
The fact that your snake just ate suggests it's probably NOT an RI. But like I said, keep an eye on her.