A.B.
My daughter did the same thing around the same time. After a few weeks of trying to figure out why she was waking up, I figured out that she just liked being up with me in the middle of the night. I ended up just letting her cry it out one night and that ended her waking in the middle of the night. I just shut her door and ours, turned off the sound on the monitor (I also have a video monitor so I could see her) and turned on our TV to drown out the sound of crying. It took a few hours but she eventually went back to sleep. She has been a sleeping though the night since and she's 27 months old now.