this are common and fine. kids do grow out of them, though i dont know at what age they stop completely.
i had them when i was a child, and so did my son. theres nothing wrong with your child, she has not had any trauma and violent tv etc wont cause them. she has no recollection of them and she wont, so thats ok too. she isnt awake, she really is still sleeping. there is some advice out there that says to watch her but not interact, i call that advice bull. you do what you feel you need to do to comfort her. ive found with my son that if i snuggle him and sing him a song, do the prayer and 'bedtime routine' that he stops faster than if i did nothing at all.
one thing that you can do is try to wake her up around the time it usually happens. take her to the bathroom, get her a drink of water, stuff thats really low key. it is thought that night terrors happen to children when they are switching between sleep stages, so if you know how long after falling asleep that she does it, great! just wake her up a few minutes before that and see if that helps
you can certainly talk to her doctor, but i assure you that its most likely normal. just do what you can until she simply grows out of it. its unclear why some children get them. it really has no definate cause that they know of. just have patience and give her comfort if that helps all of you.
another thing that could be possible is if you konw it is in a cycle, perhaps during that cycle she could sleep on a matress or on the floor in your room so that she would be right close to you when of if it happens.
good luck.
www.askdrsears.com might have some info about it, but even in the 20some years since i was a kid, there isnt anything new. shes normal, shes healthy and shes going to grow out of it. :D
its wierd that you havent heard of these before. if you get to the sleepover age and its still happening, just talk to the parent, tell them that she has these night terrors, and thought they seem scary they are not harmful, there is nothing wrong with your daughter, and she will grow out of them. the more relaxed about it you are, the better for another parent. however, let them know that it is perfectly ok for them to say no to the sleepover. you can always have a sleepover at your house instead. :D
good luck. rest assured, shes really going to be fine. :D