When she did the reverse mortgage, only those on title would have gone on the loan. She could not have put anyone else's name on the loan, unless they were over 62 and on title. If there are absolutely no heirs, she may still have willed it to a charity or a good friend. Borrowers are usually asked for an emergency contact; she may have given the name of a neighbor or a lawyer or accountant.
If there is a will, then the Executor takes care of selling the home, paying off the debts, and distributing any assets. It doesn't matter what kind of loan she took, reverse or otherwise, all liens on the home must be paid off. Fortunately, since it is a reverse mortgage, the Executor will have 6-12 months to sell the house and get the affairs in order. Also fortunately, since it is a reverse mortgage, if the home is upside down, the heirs, if any are found, will not be personally liable.
If there is no will, and no one in charge, the lender will foreclose on the home. Any remaining assets will be escheated to the State. The state takes care of finding any relatives and distributing her assets; all leftovers go to the State.
You can go down to the County Recorder's Office to see the name of the lender who has the lien on the property. Hopefully it hasn't been sold yet on the secondary market. Regardless, it still has to go through the probate process. The lender cannot entertain any offers until it officially becomes their property. Assuming you are correct that there are no heirs, the house will have to go to the bank first, then they will go through their own internal processes, including hiring a realtor to sell the home, before they can sell it to you.
If you know someone who works for a title company, they can possibly find out who the lender is and who is servicing the loan.
I specialize in reverse mortgages (CA)