Crying in sleep

So the past few nights my daughter (20 mos) has been making little moaning crying type noises in her sleep and sometimes even full on crying out and thrashing arms. She hasn't seen anything new that could have frightened her. She is getting her last 4 teeth she's missing (other than molars that aren't age appropriate) but never did this with other teeth. Any thoughts?

She sleeps in bed with us so I'm always right there to comfort her. Is there anything else I can do for her? I know everyone gets nightmares but is there anything I can do to help maybe prevent them to some extent?