I have a three betta sorority housed in a ten gallon. There are only two ghost shrimp with them now. I want to get some other fish in there, if I can. I was thinking guppies, but I don't know if that's such a good idea. Any ideas?
Ugg I don't want to rearrange my whole tank just to add another girl...
....But with only three girls your likely going to have issues. Things could be fine for now, and remain fine for a while, but they can turn on one another at the drop of a hat. The importance of having 4+ females is to spread up any aggression so that no one female is bullied to death. With three, two will gang up on one and kill her, and then the weakest of the two left will eventually be killed by the strongest. It will happen eventually if you don't have enough females.
I suggest you head out and pick up two more girls, rearrange the tank(it doesn't have to be a chore if you don't make it one ;) Have fun with it, after a little while you can always change it back too if you want.), and add those in. Thats pretty much your limit for a 10 gallon, though you could get away with a few more shrimp probably....even with just three girls I can't think of a fish that I'd recommend putting in there, other then a couple more females ;)
So that they don't have their territories already established and chase the new girl relentlessly away from "their" spots. If the tank is rearranged, all of them will be lost and unfamiliar with the setting, not just the new girl. So when they reestablish their little territories, the new girl will be able to claim a spot of her own... presumably.