Hm, that's very curious. Teething I've read is usually between 6-8 months.
Have you given her body a thorough examination? She could have chewed something she wasn't supposed to and it may have been sharp. I'd check her gums. As well, my boyfriend being the bright guy that he is, thought it would be fun to take her through some bushes. The day I saw this, I was wearing capri pants and as I walked by, one of the bushes scratched my ankle and it was sharp! And he was pulling our puppy through that! She had a couple little scrapes on her underside after that, and I've asked him not to take her there anymore. Does she have any small cuts?