C.L.
She may be teething or experiencing separation anxiety for the first time. It will pass (believe it or not). Has anything changed with her routine? Changed bed time, taken away a paci, moved? Night terrors occur within an hour of falling asleep so if it's during that time it could be that.
My daughter (almost 2) is an awesome sleeper but she has gone through phases like this with either waking up in the middle of the night or not wanting to go to sleep without us in the room. This is going to be soooo hard but it will help I promise. Let her cry it out. If you don't she knows that crying will bring you back in and she gets her way. If you let her cry it out then she will eventually give it up and go back to sleep. Stand outside the door and tell her you are there and it is okay to go night-night. But don't go in. Good luck to you!