It really depends on the snake. Our boas are all piggies and eat whatevers offered, whenever its offered. 2 of our snakes have had respiratory infections in the past (both were less than healthy when we got them). Both of these snakes ate regularly while they were sick.
I'd suggest if you think your boa may have a problem, take her to a vet with reptile experience and get her checked out. It can't hurt to rule out problems, especially since you just acquired her.