What you are describing sounds much more like night terrors than nightmares. Night terrors happen to a small percentage of children while nightmares are upsetting dreams that happen to all kids. Let me try to explain the difference because the management of these two sleep experiences is not the same.
Night terrors happen when a child (usually a toddler, like your daughter) arouses from deep sleep without totally waking up. She might pop up from sleeping, cry inconsolably, be disoriented, and stare completely ahead unaware of anyone or anything around here.
You may initially think she is having a nightmare. But she actually is in a stage of sleep where she does not dream at all. It is because she is not dreaming that she will not have any bad memory (as she would with a nightmare). And normally will not remember the episode in the morning.
On the other hand, nightmares happen during REM sleep. So children tend to remember the event. And they have little interest in going back to sleep in the middle of the night. The child needs comforting. You may even need to stay in the room for a while. At least they can be consoled.
In contrast, with night terrors, parents often try to wake up their children to comfort them. The best thing to do is just the opposite. Keep her asleep. If she is not awakened, she should go back to a normal sleeping pattern by the end of the episode. This is usually less than 20 minutes.
Night terrors eventually go away without any special treatment. The hard part is waiting for that time to come. This experience can be very traumatic for parents. But it does not represent any serious psychiatric problem.
Of course, if she is thrashing around, it is important to keep things out of her way so she does not hurt herself. Sometimes you might be able to awaken your daughter before the night terror usually happens. For the most part, medicines have not been very helpful. But on rare occasion, it can be tried.