There may already be a lien on the house if the owners are accepting public assistance to pay for the nursing home. There are also what are called "title clearance" issues -- how did they own the house and when he passed away did anyone follow through on putting title in the widow's name. The POA itself may be questionable. So if this would be a bargain, hire an attorney who can help you work through all the issues. With this kind of investment don't do it half-asked.
As long as the nursing home is being paid for out of different funds and title is clean (contact a real estate attorney and have them get in touch with a title insurance company such as Ticor or Chicago Title Company) then you should be ok. However, fraud could also be an issue and you should hire an attorney and tread carefully.
This should not be construed as legal advice or the making of an attorney-client relationship. this information is purely for informational purposes and should be treated as such.