Don't know if she is still riding or not, hence the need for a post script. RE: finding something decent for $150 or less, here are a few things on my local Milwaukee CL.

As for finding something decent for under $150, I wouldn't set out cross country touring on any of these, or ride the TDF, but all of these look pretty solid, most probably ready to ride. I actually went this route for my son 3 years ago. Bought him a Trek 800. Took three years of kid abuse, and he still rides it with me on 25 mile rides. I wouldn't let my son ride a Wal Mart bike, even though there was a time when he wanted one.

http://milwaukee.craigslist.org/bik/3888733042.html
http://milwaukee.craigslist.org/bik/3888519470.html
http://milwaukee.craigslist.org/bik/3887793472.html
http://milwaukee.craigslist.org/bik/3881973898.html

Now, buying a used bike takes patience and perhaps a good eye for quality, something a newbie maybe doesn't yet have. I really do want to hear back though. If I was wrong and the Wal Mart bike is good enough for a new rider, I am man enough to admit it. And if I was right, will remember this thread the next time someone asks the exact same question on this forum.