There are several possible reasons for her to actually ask you this question.
1. You didn't qualify her enough beforehand. Which means you should re-qualify, just say something along the line of 'actually... I'm not so sure myself! Now remind me again, do you cook?' bla bla etc
2. She gained 20 pounds since the picture she sent to you. ha..
3. She just need some re-affirmation that you genuinely like her as a person and not just looking for casual sex. Something from some of the above posters should do nicely.
4. She never actually intended it to go this far. Just having some fun online to make her feel good about herself.
5. She is not comfortable with meeting you cause she thinks you're a creep. just kindding.
Nobody can really give much advice without more info.
Think outside the box.. Or better yet, keep expanding yours
The way you do anything, is the way you do everything