First, your sister needs to authorize you to speak for her in this matter, through a limited power of attorney . You can get a form for this at any Office supplies store, like Office Max and such, though it ll cost $$$. Second, you may want to enlist the help of a consumer debt conciling services, the NON-profit ones, NOT the ones advertising on TV or radio.
That s easy.. Have your sister call the collection agency with you (NO point calling the hospital, they sold the bill to the agency and don t have any record of your sisters bills anymore), she can give them permission to speak with you and the rest you can negotiate, but keep her by your side the whole time you talk to them. Now if you want the amount reduced, you ll have to speak with them and see if they can help you with it.And if you do solve the issue, send them a money order not a check!