HSG, now rate that list as far as likelihood goes.
Also, another possibility: bipolar or straight crazy or something.
Pro tip: this one should be in the top three as far as most feasible go.
Most likely to least likely:
1. fun hater
2. bipolar or straight crazy or something
3. had to poop really badly
4. dates online and prefers short first dates
5. She is a super hero
6. She wanted to be a lady on the first date so that she could really get crazy on the second date
It's not looking good for me. 
How was she in the hour long date you had at dinner? Did she make eye contact with you? Did she seem warm/affectionate? It doesn't sound like she was crazy by any means. Shy/reserved, yes...but I don't see crazy. She may not even be the fun hater that I thought.
You could just be beginning the relationship with someone who is shy, but unleashes the freak flag when things "get comfortable." I think another date or two wouldn't hurt and she is obviously into what thunder you are laying down.
Sidenote, about a year ago I was getting pretty serious with a filly a couple of years younger than myself. She seemed cool, I had a good time with her and actually saw a potential relationship. One night, she popped in a chick flick and we watched it in bed together. Right in the middle of the movie she says: "I wish you would break my arm so we could be like this for days."
I immediately walked out and broke up with her via the phone because I didn't feel like getting stabbed. My point is what you perceive as abnormal may be nerves and what I perceived as normal clearly wasn't. You just never know if you are into a psycho until that freak flag flies.
