My toddler will not get out of bed

My 3 year old was adopted by us when she was 1.5 years old. Almost as soon as she moved in we had her in a toddler bed. She is now 3.5 years and we are having a problem that sounds silly on the surface but is very difficult. She will not get out of bed. There have been nights where I have put her to bed, and I go check on her an hour later and she is wide awake. I don't want her up every 5 seconds but if she is not tired or not feeling well, most times she will not cry or yell or try to get up, just lay there being quiet. I should also say that right now she is in her toddler bed in our bedroom. We are looking for a bigger house but in the meantime we added her and her sister to our family so space is tight at the moment. This morning I sat up in bed and she immediately popped up, wide awake, and started fussing saying "the pee is coming out". I then told her to go pee on the toilet, and off she went. I could tell she had been laying there holding it for quite some time. I tell her every day that she can get out of bed to go pee. If I get up before her in the morning I have to keep checking because she will not get up and come out without being told. It was like this from the beginning. Anyone else have this experience? Any advice? TIA via /r/Parenting http://bit.ly/2VRMzmP