When we bought Sully's crate, we bought one slightly too big. It's perfect for now...but waaaay too big for him when he was a tiny pup.
In order to crate train him effectively, we had to barracade part of the crate by putting tupperwares in there. He barely had room to lay down, but it really worked and we were able to take the tupperwares out in only a few short weeks.
But when Sully was about 7 or 8 months old, we started barracading off the kitchen and putting his crate and toys in there, with all the rugs pulled up and his crate door open and the TV on Animal Planet.
We haven't had an accident in the house since then! Isn't that amazing? We even give him the run of the house sometimes...but usually we barracade the kitchen just in case he finds something random to chew up while we're gone (haha).
Regarding Sophie, I would say that if she's been doing good with housetraining, then she deserves a larger crate. But if she starts having accidents again, move back to the smaller size. Make her earn her extra space
