When/how is mortgage interest paid on a reverse mortgage?

I just did the IRS tax return for my late mother in law, and I was shocked at how much the mortgage interest was given the loan amount.

But my wife says that's not just the mortgage interest for the loan for the first half of the year until the house was sold (she put it on the market hours before her death and it sold a week later in early July). She says it's the mortgage interest for the entire life of the loan.

I thought that sounded strange, but I haven't been able to find out by googling. From what I did read, I got the impression that mortgage interest is deducted from the payments the lender sends to the homeowner.

How does it work really?
Added (1). FWIW, where I said "she put it on the market hours before her death", I meant that my mother in law put her house on the market hours before her death. Everything had been set up weeks earlier, with a day & time for the real estate agent to put it on the market for best results. Then her health deteriorated suddenly, and the hospital called us to come in.

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