The deep skin between the middle of the forehead and the eyelid bones...
They will experience a significant change in their communication at the age of 25, perhaps marriage or separation.
(At this age it is unlikely that she would be introduced to why such a line might mean breaking off the marriage.)
Try asking people whether they suffered a breakup (a major breakup) at the age of 25? You will be surprised by the high rate of answering yes.