@maxinvasion Obviously there are already comments about sleep training. I'm not going to deny that sleep training is important.
BUT there could be other explanations for the night waking. You should speak with her doctor about the issues and tell them everything you've already tried. I wouldn't do anything like melatonin without talking to a doctor first anyway. Sleep apnea, parasomnia (sleep walking), and many different physical and mental conditions can cause night waking and sleep disturbances.
Does your child snore or have breathing difficulties?Could be sleep apnea.
Does your child have any developmental delays, odd behaviors, or social issues? Could be ADHD or Autism.
Do you or your wife sleep walk or talk? Parasomnia is genetic.
Speaking from experience, our daughter has Autism and has parasomnia, but she also had severe sleep apnea due to enlarged tonsils and adenoids which made both issues worse. She had surgery and now she sleeps better, but we still give melatonin to help her sleep through the night at doctors advice.