So sorry about the accident. She will need all the love and support she can get.
If you want people to sign it, the best way to make this neat and easy is to prepare a folder. A hanging file folder will work or a school folder. Glue a piece of fine sandpaper inside where the fabric will be.
Cut a hole in the cover of the folder the size that will show in the finished quilt. That way people can't write on the seam allowance.
Draw a line around the inside of that hole so you can see it when you open the folder.
Open the folder and draw where you want the fabric to be. Larger is better. Give yourself some room to trim.
Prepare fabric squares in very pale colors or white the correct size.
Give people the folder with the fabric inside and have them write with a pigma pen. (They won't wash out.)
Good luck. And bless you for doing this for her.