She is entering the latter stages of dementia and has already lost so much cognitive ability.
Many younger guys are driven to women who are 10 years older than they are or more, as these women are often more confident and more sexually driven and passionate than the younger women.
Should she have cut it as soon as she felt that she was developing feelings for the guy? should she continue seeing the guy, enjoy dating him as much as she can while she can, and not worry about the outcome of the situation too much, without thinking about the future too much?
I don’t think any woman can find an absolute and unequivocal answer to this question, and I frankly don’t believe that such an answer exists, as it would heavily depend on that specific woman’s goals and needs at that specific point in her life.
Women who belong to this category will not be happy sticking around a guy, if they know in advance that it is not going anywhere and has no potential to turn into an actual partnership.
Only you know which category you belong to or which category you want to belong to, and once you determine which approach fits your life philosophy, you are likely to make the right choice for yourself given your unique situation, as well as what you need and want at that specific point in your life.