I think you're pretty much out of luck on this one Kelley. I'd call it a learning experience, and let her come take the cats, and then NEVER deal with that group again. If the cats are costing you more and more every day, it only makes sense to let the rescue come pick them up if you are not willing to continue to pay for the vet bills (and you're not willing, you have said many times that you expect the rescue to pay these bills, not yourself). I think you will recall several of us on the list advised that you should just return the cats to the rescue back when you first posted. If you don't want to return the cats, then you will have to adopt them, and pay the adoption fees (and eat the costs up to this point). A foster home is just that, a temporary home for the cats until the rescue can take them back, or until they are adopted (whichever comes first). It is your duty to release the cats back to the rescue if you are contracted as a FOSTER home. All their bad policy aside, that's what it comes down to, you CANNOT keep the cats unless you ADOPT them. You have two choices, either call it a loss, pay the adoption fees, and keep the cats (assuming they will approve your adoption application, which they may not at this point); or return the cats to the rescue and end your foster contract with that rescue group.
Phaewryn VT low cost Spay&Neuter, and Emergency Financial Assistance for cat owners: http://ucat.us/VermontLowCost.html Special Needs Cat Resources: http://ucat.us/domesticcatlinks.html