I'm sorry, I'm old and feeble minded sometimes... So... once again, the other hens ARE using Aprils coop, but chasing April and the chicks away from it? Chickens always "fight" to establish a pecking order. The only way to lessen this (and other behavioral issues) IMHO is to give them more space. I have no idea what size April's coop is, or how many birds you're trying to fit inside it. Large fowl birds need ~4 square feet per bird of floor space inside a coop. More is obviously better. Multiple feeding and watering stations will also allow for less fighting as everyone can eat and drink more easily with less chasing/fighting.
April should be protecting her chicks from the other hens until they are old/large enough to fend for themselves. As RR said above, maybe moma hen is done and the chicks are on their own now? And, I'm sorry to say but some chickens are just plain bullies. This being the case, there is only one option... remove the bully, one way or another.