I do not know of any "free" places. I do know that 11 is a critical age as I am sure you are aware since you have a 14 yr old. I have a 13 yr old daughter. We just got back from shopping again because she is planning what she will wear the first week of school. It is very important to them.
I don't exactly understand if you can't take her shopping or if the shopping is out due to financial issues. Maybe she can use something of your 14 yr old's or your 14 yr old could babysit for you and you take her to the Goodwill shop, Thrift Store, garage sales if it is $$ issue. Have you tried Craigslist? There is a Plato's Closet in Plano Spring Creek/Alma that has a lot of the "in" things for teens (Abercrombie, etc). I have sold some of my daughter's things there. You can get good $50 jeans there for about $12 and good deals on tops too.
I would get a couple pairs of jeans, some tees and sneakers. She will more than likely have PE!! After school starts, she will see styles, etc that she might like. I fully expect to go shop again after the 1st or 2nd week of school.
I would offer some of my daughter's old clothes set to go to Ebay but she is a 00 in jeans and size 8 shoe. What I have is all size 10 slim-12 girls. I wear size 3-5 Jrs so I don't have anything either. Hopefully you'll have some luck quickly!
Hope some idea I had might help you.