Is the enclosure in a busy location? Or subject to loud noises (vibrations from speakers or something)?

All other husbandry issues being ruled out...the primary reason why a BP won't eat (especially a young one) is if it is feeling insecure.

Things I would try:

--Make sure the enclosure is in a quiet place away from normal family traffic

--Make sure there are no bright lights shining directly into the enclosure...and that it is subject to a normal day/night cycle. (Any ambient light is plenty...they don't need a "bright sun" to simulate the daytime for them.)

--Take some sheets of newspaper and crumple them up into loosely wadded balls and fill the entire enclosure with them. Not crammed in there...but just loosely filling up the empty space. ... After a week of that, drop a fuzzy mouse in and leave it completely alone overnight. ....check the next morning to see if the mouse was eaten ....if not, remove and try again the next week. If so...continue with the same practice the following week. After a couple successful feedings, you remove the balls of paper one or two at a time after each feeding until the enclosure is eventually empty of them.

I realize this is a long-term solution and you're looking for a "quick fix" before putting the snake in the hands of your friend...but changing homes is only going to add to the stress. If you can enlist your friend's aid in the "newspaper trick" I think it will really help.