Of the bikes shown I'm partial to the Jamis. I've test ridden this steel bike bike and like the ride. But really, why the waste? Her commute is very short for the price being considered. I ride 12 miles one-way on a $425 Marin Larkspur. I'm just getting warming up after 4 miles and 15 minutes.

Does your sister plan to ride beyond the commute?
If the answer is on most days - no - then she can get a decent and comfortable new bike for her short commute between $400 and $500. I'm mean - who pays for super performance for a 15 minute ride to work?

I think Knho's advice on the above thread is good if she truly plans on riding alot beyond the commute, but my intuition tells me that if you are getting advice for her then she is a relative newbie and that one modest comfort bike will serve her well for years. Also all the bikes shown are fine bikes but for some reason I am wondering if your sister has test ridden them. That direct comparison of 20 to 30 minute test rides on each over a weekend will tell her more than recommendations on this thread.