I'd be pretty sure having some characteristics that are between genders, or just infertility, can happen in any species. It's even seen in much simpler animals such as insects, usually not that pronounced that there is really a mix of two reproductive systems, or an appearance of the one but organs of the other, but often more subtle, like hormone levels or receptors not reacting to hormones.
So I cannot show any proof that exactly hermaphrodism happened in exactly a bearded dragon, but in general, animals with both male and female characteristics, or just the reproductive systems are not working, aren't uncommon.
Possible but not likely. What do you mean by outward sex characteristics though ? Can you post pics with her tail arched up high while she is flat on a table or bed ? Arch the tail up to a position similar to a dog's tail when they are excited.