Rude awakening for the sisters, but it isn't her house unless she's got the money in the bank to pay off the reverse mortgage. The house belongs to the bank until that is paid off either through sale after death, the note being paid off by relatives, or foreclosure. BTW, if they don't pay the insurance or taxes or if they move out of the house certain periods of time, that triggers loan default and the bank starts foreclosure proceedings on it. Taxes and insurance are usually the big "gotcha" because most folks are so used to having that taken care of with escrow payments when they have a regular mortgage that they forget about it.
Keep that feather in your cap for future use.