Hello,
How does she fall asleep when she initially goes to bed? I agree, that you should not leave her to CIO as that will probably make matters worse. This age can be so tough sometimes with developmental things going on, teething, etc.. My ds who is 2 still wakes up once a night. He just wants a drink of water, so it is relatively quick. My only suggestion would be to go in and reassure her when she wakes during the night, keep it short with little interaction, try not to pick her up, and remain consistent with how you respond to her.
Hope this helps a bit, and good luck!