15 month old won't sleep

Everyday so far for about the last week and a half my daughter has been waking up around midnight to be up for an hour or two screaming in her crib. I don't know what's wrong. It's not her teeth, she gets plenty of play time, big meals. I'm at a complete loss. And to top it all off, she kicks and screams at me every time I try to rock back to sleep. It's diving my wife nuts with frustration and I hate feeling so helpless. What can we do to get her to sleep through the night again? Or at the very least, how can I support my wife better through these proverbial fights with our toddler?