The nightmare phase is usually short lived. Try not to let her be overtired when she goes to bed. Do not dwell on the nightmares. Maybe even not talk about dreaming before going to bed as that might have her scared falling asleep if she knows her dreams are not nice ones no matter what she starts out doing.

Unless the child actually screams and wakes herself up let her be. Trying to wake her up fully may actually make it worse. Read up on night terrors which a form of nightmares that kids get. Some will even sleepwalk during one and then not remember it in the morning.