Hi AmtotheBurr,
I can only comment on a recent experience when I bought a female Betta for my daughter. In the shop I had a choice of 2 female fish and the owner pointed out to me that one was loaded with eggs and ready to breed, this was the very reason we were buying the female as we have a male already who is making nests every 2 or 3 weeks. We choose the other fish becasue she was the correct colour strain for our male, but, yes it is possible she is laden with eggs and ready to breed.
Richard.