"But is there any Checks and Balances for these rescue groups? maybe having the IRS yank the non-profit status since they don't fulfill the purpose they claim too?"

Sorry, I don't know how (& if) the US rescue groups are regulated.
But on the question of fostering a dog , it's useful to check what a group's follow-up procedures are. Some groups which foster locally take the responsibility for delivering the food to the foster carers. That procedure keeps the communication up between group & fosterer.
Shortnen is a lovely looking dog. Good on you for taking such good care of her.
Marie