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.
Often, a younger guy and an older woman would “decide” upfront that their relationship will be casual, and that they should not expect any commitment from each other, because they know that the end of that relationship is inevitable because of the seemingly irreconcilable age difference.