Are you sure she's not working on her 2 YO molars ?
It was not as bad for us as you describe it but 2 weeks ago, my 2 YO went through a short spell of 3 nights of being awake for 2/3 hours for what seems to be no apparent reason. My hunch was that, whatever happened, he couldn't get over it immediately and got himself more and more overtired. So over that weekend, I let him have as much sleep as he could get and followed up with him going to bed earlier after that. One week after that episode, he was up again but this time he was able to tell me that his teeth were hurting, so at least there was something I could do about it.
I hope it gets better for the two of you. It must be quite disappointing when your previously good sleeper starts having sleep difficulties - at least mine has been consistently poor