My MIL is now at the age which this woman will be when her child is in her early teens. We have just put her in a nursing home.
Mentally, she is as well as can be expected of an 82 year-old- she does not suffer from dementia or Alzheimer's or anything like that. But that is still a long, long way off being as mentally resilient as a 50-yo.
You couldn't, for instance, have a shouting match with her- she is just too frail. SO what will this 14yo do- forego the teenage stage because her Mum is too old?
MIL is beginning to find it much much harder to make decisions- her mind is simply less elastic. She has got to the stage of life where she needs to lean on other people. Us. Which is fine, because dh is a grown man. But what about a 14yo who needs somebody else to be in command.
Most healthy 82yos I know are beginning to get physically timid- again not ideal when you are bringing up teenagers.
I am sure she will make arrangements for if she dies. But what if she doesn't die, but carries on living with her child. IME most frazzled grandmothers looking after grandchildren are actually in their 70s rather than their 80s, that makes a huge difference.