All good advice so far. Just get something you like, are comfortable with and have someone qualified fit you for the bike. Perhaps consider not spending too much money on your first bike as, in my experience, many people, 12 months after buying their first "cheap" bike, love cycling and want something better - hopefully, by this time you will have a good understanding of what suits you. Just as long as its not "too cheap", breaks down all the time and puts you off.

Also, how "heavy" are you up top? My wife finds the aggressive forward lean on some bikes uncomfortable after a while, and she prefers a more upright stance on a bike. Have you tried riding a more aggressive bike - maybe Mary Poppins sat up straight for a reason?

By the way, women who cycle are HOT! ... its great way to tone up.