Amy's crack in her wall (dr who) makes no sense

The crack eats people… but only when convenient. Sometimes, it erases people from existence. Their memories vanish instantly. With Amy, it took longer. And how did the doctor remember Rory after he was consumed by one? He shouldn't have. Other times, the crack selectively targets Amy's parents and aunt, but not her or even Rory or Mel, who spent time in her room growing up. The doctor also said it was eating away at her life for a long time, hence why she couldn't remember where her family went. How can she exist without her parents? She can't. How does her Aunt know who she is/raise her if she never had siblings? How was Amy able to keep the house, go to school, etc growing up when all her records should have disappeared, because hey, no parents! Therefore, she shouldn't exist either. The Doctor later claims she'll have the universe pouring into her head at night right before he closes the crack, which doesn't make sense. It showed up at around 7. And with it closed and never existing along with that future, she's completely normal. No, ridiculous, she "remembered him" back into existence. She wouldn't have any memory of him whatsoever. In fact, this Amy would be completely different. A reboot version if you will. An upgrade that never happened. She was normal. Grew up normal. Her entire arc doesn't make sense. What do you think?