Love this whole story!
I like the idea of something for both your DD and G ... so here is my suggestion.
Snip the pants apart as you have been planning .... and applique the front onto one quilt and the back onto the other quilt.
The other side of both quilts could be a more traditional pattern or just a plain fabric.
Both girls would then have options as to which side they want to show as the front.
The pants side would be like a hidden surprise if the other side was what people see.
That was my idea ... but I do think GingerK's suggestion is a wonderful one.
That is, if you want to include the others from the dance "family" in this.
However, this might start something you may not want to do ...
... with others wondering, so why don't I get a quilt.