I'm sorry and understand her disappointment. From many many years observing and being a team Mom in a variety of sports I'd like to offer unsolicited advice. Hmm...I do have that tendency, lol. If it is possible (I don't know her personality, of course) have a conversation with her about the opportunity she now has to impress the Coach with her enthusiasm, dedication, selflessness etc. etc. as Manager.
I have never met a Coach who didn't observe everyone involved with the team. If she can show that she really is stepping up to the plate to help the team every day and she takes every bit of time to improve her own skills I am positive she will have a much better chance of being chosen next time. on the other hand, if she appears disappointed or distracted etc. she will be indicating lack of team spirit. I've seen it work both ways. Of course genuinely helping the team members is likey to endear her to them also. It's hard to do but there are life lessons available to her. Our world, her school, the church and businesses of all sizes operate only because of support personnel. Sending cyber hugs to you both. DDD