3.9 y/o Awake at 2 every night, normal?
Well, my 3 y/o does wake up right around midnight or so almost every night - but she just comes into our room and goes to sleep whenever it happens. Don't think she's ever gone without waking up then. I have noticed that she'll often be waking up and need to pee (sometimes she uses the bathroom on her own, sometimes not and I nudge her). Could somehow be related to that - her bladder still growing, it waking her up whether she realizes and goes or not? Could she be having growing pains (in her legs) waking her up? Both those are pretty common, and she might not recognize them at the time.
We're sleeping more like 830/9-7/730 here with one waking, so that's roughly the same amount of time. My oldest slept a bit less (more like 930/10/1030 to finally get to sleep and could wake up at 7-830) so it can absolutely vary or change.
Oh, that would make a lot of sense to me too kellyandbean then, that it's night waking because she needs to go pee (or is uncomfortable being wet at night now and having more trouble getting back to sleep?). A few nights of "Hey, mommy is going to carry you to the bathroom to try and go pee" might help. I know I did that with dd1 for a few nights in a row, and it would really help her work toward being dry all night for a few weeks and there was less waking up at night. Or we'd wake up and change her nighttime undies because she had a hard time falling asleep at times with them wet (we used cloth nighttime trainers, so this may or may not be as easy to do for you?).
For us it took a few rounds of trying this out until night waking/wetting went away, so keep that in mind. If it really doesn't work to wake her gently to get to the bathroom, give it a few weeks and try later. The times when it actually mattered to my dd went a lot smoother for us, doing this.