Has she ever slept consistently through sleep cycles though? If she has been waking often through the night for a long time, it might be more an issue with not knowing how to resettle herself instead she gets to the stage of sleep and jolts herself into awakeness. If it is something that has only started more recently (and not just become worse more recently) then it is probably more to do with environmental factors like sleep, illness, noise or being in a different sleeping environment.

My kids wake during their sleep cycles too when they are sick but since they are bit older, they can tell me it is because their throats hurt or their noses are blocked so being uncomfortable wakes them up. They also do it when they teeth because that is when I think they notice the pain. Teeth move around when you are sleeping and your muscles relax which is why babies and toddlers usually cut their teeth through the night. I think when they are in a deep sleep, the pain isn't as noticable but as soon as they move into REM sleep, they wake up from the pain.

Otherwise it could be to do with her sleeping environment in general. If she is not used to waking up in her own room, or she is in a new room or there is a new noise (even a dog barking, reverse cycle airconditioner for heating? anything). Also if she is too hot or too cold ... all those things could be causing her to wake in that REM stage instead of resettling.

Do you have a night light in her room? I found a night light actually helped my kids sleeping issues a bit. Also leaving the door open. Once they got to two, they didn't like being in a dark room with the door closed anymore and would wake up distressed. So that is something else to consider.

I am just throwing possibilities out there. It could be any of these things or none of them, but they are worth assessing just in case it is environmental