Regurgitation can happen for many reasons.. from what I understand the prey item could have been too large (Have you fed her that size before?) The temps could be off in the tank, which could alone cause regurgitation if it's not warm enough but it could also stress the snake which could also be a reason. Was it a F/T? Perhaps it wasn't completely thawed. Any additional info you can provide would probably yield a better root cause... I'm sure a more knowledgeable member here could also offer more insight.