Today becomes her last day of care until back payment is made or you will be working next week for free too. If she is going somewhere else you pay is probably being used as the deposit. Email her and let her know payment is due by noon tomorrow and there will be no further care until the money is paid.
You won't get paid more than likely but you also won't be working another week for no money. Collections is an options but just because you get a positive settlement doesn't mean you get any money or that the fee to the collection agency makes it worthwhile. Sometimes hitting them where it hurts and pulling care for non-payment is just as effective at making you feel better. But please don't do care next week and let her continue to string you along with promises of payment.
Hopefully you have a replacement child already lined up and if not then ads should be put up today announcing new start date.
No receipts unless a payment is made. Until she pays up for the back two weeks you are unable to complete the receipt so don't give her one. Come tax time next February you will owe her a receipt for any amounts paid to date but you do not have to give it to her now. I would hold the receipt for ransom so to speak and hope she pays towards the amount owing in the meantime.