I know how you feel, I spent many years quite a long time ago "rescuing" all the sick/homely/torn up bettas I could afford. ;) It really does feel good when they finally start to grow and fill out and look really good compared to how they started. Plus you get the satisfaction of having rescued an animal from a pretty horrible life. :)
Mine, if I could get them healthy (most were sick when purchased), would grow and fill out nicely in a few months time. Many never got terribly big, but they would color out and their fins would get fuller over time. I would think that your girls will be the same way. :)
As for putting your big female in with the small females, I've never kept females, but I think that ZackyBear is right, that it would only lead to disaster. If you can't separate them all individually, do you have a large enough tank for all the small girls to go in together, so they could have their own sorority?
Good luck with them!! :D