She's pretty much priced at about the right price from what I see on ebay.

The cheapest trek 1500 with 9 speed 105 sold for $561 + shipping - but it did not come with wheels - everything else sold in the $675-800 range:
http://cgi.ebay.com/TREK-1500-Road-B...QQcmdZViewItem

I don't know where you live, but around here you can get $650 or whatever for a mostly unused bike with tiagra level components. The trek 1500 that you're looking at has 9 speed 105. HOwever, I'm in a crowded metropolitan area with lots of yuppies and maybe your local market has less people with money

I sold a 2004 trek 1500 in the fall for $850 - but it did have a spare wheel and a few other things.

If you can talk her down to $600 - great, but I think $500's too low.