Try www.4wallsinphilly.com and www.philadelphiaweekly.com I always recomend the Sterling at 18th and Kennedy Blvd., a really nice building. It is not a loft but the rooms are huge with wall to wall windows and it is a 1 block walk to 1818 market. She/He could come home for lunch.
You can catch a bus from 1818 market every 5-10 miniuts that will take you to curtis center.
There are several buildings that offer temporary housing downtown until you can find a place. try www.oakwood.com
A blind, long distance apartment hunt is not a good idea. You have to see the unit you are going to rent. Also there are no parts of downtown Philly (they call it "Center City" here) that are not safe.

PS-I did a little internet shopping myself just for fun and saw that many places don't bother to advertise at all. I guess the rental market here is still pretty tight. A lot of rental buildings have converted to condo so that pushes vacancys even lower. All the more reason to go the temporary route and wait until you get here.

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"Some people use change to further their careers and some people use their careers to further change." I voted for change once.....we ended up with Jimmy Carter.