Lapses in memory can be proven false. It might be difficult, but sometimes it can be shown a person remenets exactly that which they once claimed to forget.
Perhaps they should compare the failure to recollect against any emails that that she received or sent that bear upon the question, especially if those emails were after her conk on the head.
There was a line from a Paul Shanklin parody, “I can’t remember, my mind’s in a blender...”
Rush played it on several occasions.
https://www.youtube.com/watch?v=eWQureIC1QM