This sort of thing happens ALL the time at DD's gym. I think that nearly every parent on DD's team has, at some point, felt the way you do. If your DD stays in the sport long enough I can almost guarantee you will feel this way again. And again. And again.
Sometimes the decisions about training groups, move-ups, practice schedules seem really unfair. Despite the usual sentiment on Chalk Bucket, I believe that sometimes they truly ARE unfair. Sometimes girls are slighted or overlooked, or the coach is playing favorites. But, in many cases, there is a method to the madness. Or a limit to the number of girls in a level or group. Talking to coaches about these things is rarely productive.
Ultimately, what I am trying to say is that if you just can't handle feeling that your child is being treated unfairly, your DD needs to find another activity
FWIW, the longer my DD has been in the sport, the less these things bother me.