Elizabeth Is Missing

It was well written and kept me interested, pulled a couple small twists. But I just don't find the connection between the two stories to make much sense. What, she didn't know where her sister was until 70 years later? She kept it in her subconscious all that time and suddenly with Alzheimer's it comes out? I don't buy it :/. I felt like there would be a more logical connection between the two stories but that was never resolved, and not in a good way that keeps you guessing (see previous comments).