I would not have made the quilt in the first place. But then I do not have much time and less money to be making expensive gifts for people I love, let alone those I do not like.
OP said she used fabric on hand for much of the top, but that fabric was paid for at some point in the past, unless it was gifted to her.
I would not send a bill, but I might consider calling up the sil and saying, Okay I have the top made, but I cannot afford the quilting. Offer her two choices, 1 - you can look up the names and numbers of LAQ in her area and send the flimsy (I would not send batting and backing) with the names and addresses and she can do the rest, or 2 - tell her it will cost X#$ to pay your local LAQ and you will send the quilt in once you have received the payment (in advance only).