In reading most of the answers here there seems to be relatively little acknowledgement that she was quite possibly dealing with a person who, at 80 years old, has some level of age related mental impairment that is effecting judgement and impulse control.
If a molestation was attempted on me by a fully functioning adult then all bets are off with respect to being discreet, and let the chips fall where they may, but if I am dealing with someone in their 80’s making an out of character grab at me, and muttering “nice”, incipient mental issues are probably where I would go re putting that situation in context.
This does not excuse what the old person did, and everyone will deal with the situation of being groped by an elderly person differently, but for those castigating those posters who suggest than this particular situation might have been better handled on the down low, you might want to step back and look at the overall situation.
It’s not at all unusual for someone who is 80 years old to be on the leading edge of senility. People in this gray zone are still quite mentally functional, but they also do all sorts of odd and embarrassing stuff that is utterly out of character for them when they were younger. Being sexually aggressive is often one of these behaviors.
How do you handle this in mentally impaired elderly relatives? I’ve seen my elderly relatives do, or attempt to do stuff re being inappropriate that may well have gotten them arrested if allowances had not been made for their age and disability. It’s not like these things were kept as some dark family secret, the situation was discussed with other family members in the context of the impaired person needing supervision or some level of control being necessary if they interacted with others.
This is not to diminish being sexually groped, but being groped by an 80 year old family member who is on the down slope to senility is something people can (and do) handle with discretion within families in the interest of preserving family relationships. For better of worse allowances are made for misbehaving elderly people throughout human society.
Only the OP was there and only the OP can decide what is right for her to do, but there are variety of different ways to handle things, and keeping a confidence about an elderly relative acting out character and groping her, is not any more wrong than the OP was right about discussing it.