sleep help

I believe my almost 9 month old needs to learn how to fall back asleep on her own. How do I do this when she stands at the edge of her crib and cries? Do I just let her go until she falls asleep? Do I change her diaper then put her back in crib? She goes down easy at bedtime it's the middle of the night that has become a nightmare. I'm doing something wrong but not sure what and we are getting desperate for help. She still has no teeth so we attempt to use pain gel or Tylenol somethimes thinking that's why but we are lost.