Two parts to my reply. I have extensive experience in polygraph and memory from my employment.
Polygraphs: while they are not admissible in court for many reasons, they are an interesting and helpful tool in gaining insight into truthfulness of response patterns. By using those patterns, we can surmise the likelihood of the truthfulness of one response - so in looking at this one question, we can say "looks deceptive" or not.
That said, quite often the most interesting and useful information was gleaned in the pre-interview process. I cannot tell you how many times we had people confess to drug use, lies on the application, theft, and one time we had a guy confess to seven rapes (yes, seven) during a pre-interview process. (We were screening candidates for law enforcement or clearance positions).
So it’s definitely quite common for the polygrapher to get a confession and a "sudden gust of recall" prior to the administration of the test.
I have a specialization in memory and cognition in my practice of over 30 years, so could speak for months on this. So will try to be brief.
Memories are stored and maintained based partly on level of importance. One of the things that the brain uses to determine what level of importance a given memory has is how many times you retrieve it (other factors may be how it relates to life safety, personal enjoyment, for example). So, think of your address - you write it down at first, but since you retrieve it many times, you just commit it to active memory and can retrieve it at any moment because you use it so frequently.
So, the opposite is also true. You store a lot of memories that you do not retrieve even one time. Like, what did you do the evening of February 4, 2004? Unless you got married that day, or were on a cruise, you probably don’t remember. But maybe you could, if we figured out that something happened on the 3rd, and we worked forward from there. But generally speaking, the brain doesn’t place importance on many things if they are not retrieved and used. Ultimately these things are put in a dustbin. We call them forgotten, but there could be something that triggers them with the right memory - perhaps something that is stored neurologically adjacent.
So knowing this, if the WW in this situation has not spent time recalling this affair, it is absolutely reasonable that she does not recall details. The details may not have been important to her (if she was emotionally invested the emotional aspects may be more memorable to her than times and places). She may not recall exactly how many times, where, when, etc. Those details may be vague, and may flow into one another, as the brain may very well have them stored together as one "episode" by this time, 48 years later. This would be a normal process of consolidation of events in memory, not unusual. Maybe a good therapist trained in recall could help tease it all out, maybe not.
Also know that our memories (even people with "great" memories) make errors of attribution, sequence, location, detail… It’s normal. It is not deception, just how it works.