We took her to our own vet today, and he says she's more like 8 months old, and he expects her to do some filling out over the next few months. He doesn't think she's going to get any taller, and said he thought she was probably all beagle. So, all of you and the people at the Humane Society are probably right, and I just got thrown by the fact her muzzle isn't shorter like I'm used to. LOL

Thanks for all the replies, though!