Related to Why was Susan treated so unkindly?

The children were in Narnia a long time, at least as far as time in the UK goes. By some counts at least 15 years even if just for the first time, not to mention their later few journeys.

The timeline seems to be:

• 1940 - Age 12, spend ~15 years in Narnia
• 1941 - Age 13, spend ~1 (?) year in Narnia
• Age 19, no longer believes in Narnia

It seems unlikely to me that someone would forget a large percentage of her memory in a relatively short period of time.

Is there an in-universe explanation as to how Susan could forget or come to believe that Narnia wasn't real even though it was such a large percentage of her life? Is there a "Narnia time" effect? Or am I misunderstanding how long they were actually in Narnia?

Related to Why was Susan treated so unkindly?

The children were in Narnia a long time, at least as far as time in the UK goes. By some counts at least 15 years even if just for the first time, not to mention their later few journeys.

The timeline seems to be:

• 1940 - Age 12, spend ~15 years in Narnia
• 1941 - Age 13, spend ~1 (?) year in Narnia
• Age 19, no longer believes in Narnia

It seems unlikely to me that someone would forget a large percentage of her memory in a relatively short period of time.

Is there an in-universe explanation as to how Susan could forget or come to believe that Narnia wasn't real even though it was such a large percentage of her life? Is there a "Narnia time" effect? Or am I misunderstanding how long they were actually in Narnia?