Maybe something like a used Specialized Dolce. That's what I had as my first bike. It sounds like she'd appreciate WSD, since she's all legs. She's probably around a 48-50 cm. Call your local bike store, because some of them take bikes back for upgrades, and resell them, so they have a used bike section you may not know about unless you ask. Or, try Craigslist or Ebay. You might even find one here.