She is an issue, but the root issue is work ethic. Basically the thought is that BHH could transfer somewhere else and would be handled with "kid gloves but still get lots of playing time" as opposed to Barnes not being one to baby and coddle guys.
Mom is difficult to deal with and isn't going to help in that department apparently. I wasn't given any specific story and honestly I didn't dig that much when that was shared. I assumed its a classic "crazy helicopter mom" type of deal.
To summarize: you've got a kid that struggles to self motivate which is a massive issue for Barnes who is a notorious tough coach, that affects PT, mom doesn't think the tough coaching is the best for BHH and doesn't like lack of PT, therefore you have a kid that potentially won't be here and a parent that will enable the transfer onto supposed easier and greener pastures instead of urging him to work through adversity.