I am using a good quality quilting cotton, so it's a little thicker.
I'm going to go ahead and do it like the pattern calls for. I think to double the fabric would make the ruffles too thick, and fray check might be scratchy, and might show since two of the ruffles have black background.
Thank you SO much to all that replied. I'm hoping the bias will keep the raveling down to a minimum, and will tell Gabby's mom to hand wash the outfit.
Sheesh...children's patterns sure have changed a lot since I last made them!