There could be several reasons behind that :- She may need a feed, she may want your comfort etc.
Tips To Help Your Baby Sleep Better:-
You can make your child sleep by creating proper environment for him or her. Make sure that your child is at comfort and the temperature is normal, not too high not too less
Breast milk has hormones that activate melatonin (hormone that causes drowsiness) during night this hormone is released in larger quantity. Hence, at night try to breast-feed your child instead of using bottle milk.
For your help – please read this article:- Baby Sleeping Strategies – How To Make Your Baby Sleep Faster