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If she does get a RM would it wise to put some of the money into a ROTH IRA?
No. She's 70 - she does not need to save for retirement, and there's not enough time to benefit from the tax savings on growth. Plus it is generally not wise to "borrow money" against your home to put it in an investment account, especially one designed for retirement.
A reverse mortgage is essentially borrowing money against your house slowly over time. Yes you don't "make a payment", because instead of paying the interest monthly it is pulled out of you home equity (meaning you get less back when you sell the house).
You could do the same with a HELOC by just borrowing enough to cover the expenses you need plus a little more to cover the minimum payment. It's a manual step that she may not like, but it's more transparent that "hiding" the interest costs in the RM. OR she could take out a full equity loan to get a lump sum, which would have higher interest costs but would be easier to manage since you only have to "borrow" once.
A more drastic (but cheaper) option would be to downsize and cash out some of the equity to use for expenses, but I completely understand that this is not a simple answer emotionally.
HOWEVER, this is all dealing with the symptom, not the problem. The problem is she has more expenses that she has income, and presumably has no savings (just her home equity) to cover those expenses. I would also look at expenses to see if there's anything that she could cut, or if the heirs could cover more expenses themselves rather that adding debt to cover them.