Do you know what he was trying to feed her? When you say that he assist fed and it did not work, what did not work? Was he just unable to assist feed or did she regurge?

If I were you I would setup a small tub for her, something like a 6qt hatchling tub with proper heat, humidity and a small water bowl. Leave her and let her settle in for about 7 days and get a live hopper mouse for her. If the live hopper doesn't work try it again p/k and then just leave it in with her overnight.