There are several possibilities. She could be teething, or have gas. She might just be going through a phase. It is also possible that she is now having nightmares. If it continues, you should discuss it with her pediatrician.
It's not unusual for toddlers to go through phases where they will wake up in the middle of the night. It could also be teething with the 2-year molars.
She could be getting her molars in. Those are the most painful of them all and some babies while teething will wake up during the night while teething.