I put my then 1 year old in a twin bed on the floor of her brothers room. I used to nurse her to sleep. I wanted her to feel warm, yummy feelings as she dozed off to sleep. I wanted her to feel safe and secure at night. (I don't believe in CIO.) If she woke up in the early morning, I'd go and lie with her, to help her relax and fall back asleep. When she was 2... she would quietly walk to our room, knock on my door and I would quietly walk her back (around 5-5:30am) and lie with her and she'd fall back asleep, and so do I.
She is 4 now and we still do this from time to time. Works like a charm so I have zero complaints... compare and contrast to my friend.
My girlfriend has the same age daughter and let her CIO during infancy. After that stopped working, she'd have to drive her around the neighborhood to get her to sleep. She still does this sometimes. Sometimes her daughter wakes up at 4am or 5am and can't get back to sleep. Cuddling doesn't work. That happened to her this morning (her daughter was UP at 4am).
I don't recommend letting her cry because all that is doing is making her WIDE AWAKE and unable to sleep completely.
You don't want to take her into your bed, because then she'd get used to it and most people don't want that.
So I solved it by making her bed BIG. (My children never slept in their cribs. Our son was in our bed till age 2. Our daughter till age 1. Then it was to their own twin beds.)
I wanted to make her bed "her favorite" and it is.
Good luck.