Dear C.:
I would simply do what you are doing now. Post this information on as many BBS's as you can, let your friends & relatives know how insensitive this company is.
You can also write to the company directly, see if you can get an Internet petition started. You would need 25,000 signatures to make an impact on a site like cafepress, they have been around awhile. Even with a petition, they are likely to do nothing.
Not giving your patronage to their site is your own way of not helping them be insensitive and rude.
But, I think personally that just telling everyone you know that they sell material that is offensive to the Disabled community will do a lot...remember that in business even bad press is good press. By posting this information on BBS's you will drive traffic to their site, people may not buy the rude shirts...but may still grant them their patronage.
You have to do what ever you feel is best.
At the end of the day it is what it is and they do have protection under the 1st amendment.
I am in a wheelchair and before writing to you, I went to their site to see just how bad some of their stuff is. I personally was not offended as I KNOW I am a person first and disabled 2nd, my disability does not define me. Just as it should not define your friends daughter. She is a child who happens to be blind. If she is referred to as a Blind child all her life, the disability will define her. You cannot let that happen. We are people with disabilities, not disabilities with people.
Best of Luck whatever you choose,
J. T