She's not in a draft, or have light shining on her?

My DS is the other way round, will sleep in a cot (although he is in a toddler bed now) but would wake up every 1/2 hr or so at my Mums where he slept in a port-a-cot. She now puts him on the spare bed and no issues whatsoever.

If you think it might be you waking her up, maybe try moving her cot away from you to another room or outside the door to see if that helps?