legzzalot,
The National MS Society has S'Myelin for kids which you and your daughter might find helpful.
http://www.nationalmssociety.org/mul...lin/index.aspx
Since I was dx'd before having children my kids have grown up with the disease. We never told them Multiple Sclerosis or MS, I didn't want them to hear those words until absolutely necessary.
Your daughter is only 6. My first thought was to tell her - MS is what makes it hard for me to ___ (fill in the blank) and leave it at that...if possible. If you keep answers short and simple she will probably go OKAY and be on her merry way. I believe in short and simple until she is older and wants to know more.
Just some thoughts from someone who has raised 2 kids with this disease