Boas don't need 90 degrees. I keep mine around 86 warm side and cool at 78-75. Might be tad too hot, I would reduce your warm side to 88 and cool to 80/78.
What was this boa feeding on before?
What was the first meal with you? how did she take it?
Is there a lot of activity around the tub/tank?
Are you offering at night? Have you tried leaving the feeder in overnight? (assuming f/t)