M.,
My 10 yo son suffered from night terrors from the age of 2 until 8. Hopefully I can help you - but I want to make sure you know the difference between night terrors and night mares. Night terrors happen usually in the first few hours of sleep - when your body is in the deepest rest. They can go on for 20-30 minutes and yes, the child can appear awake, but they're actually sleeping. My son even did a bit of sleep walking (we put bells on all the doors so if he tried to leave the house we could hear it). It's very difficult to wake them from having a night terror, but it's possible. No it's not dangerous to wake them, but if you decide to do so, you must do it until they're fully awake. Night terrors are not kept in memory also - the child will not remember them.
Night mares happen in the last few hours of sleep when the body is preparing to wake, they only last a few seconds to a few minutes long and the brain does retain memories of them. So if your child is fully awake and seems afraid of what just happened or can tell you anything about it, then it's likely a night mare.
When your daughter is having a night terror and she makes movements or sounds like she is not awake, but you know she is having a night terror, take her into the bathroom and put a cold rag on her face, talk to her sternly and hold her close. Offer her a drink and get her to say things to you that would make sense to her like "what is this? Is this your sippy?" Usually during a night terror, they will speak and not make sense, my son would often talk about a dragon or something but in a weird way like "the dragon - outside sun - flying hallway" and you just knew he wasn't fully awake.
I would go through periods of him having night terrors for a few nights and then it would stop for a few months, but it went on for 6 years (it was worse in the beginning and gradually got better). It very rarely scared me, since I knew how to handle it, and he fortunately was a good sleeper so he would go back to bed immediately following. But he never had 2 episodes in one night - and most the time the night terrors happened before I went to bed so I was not woken much in the night from it.
I would certainly talk to your pediatrician about it - but there's not much you can do, just ride it out and learn how to handle it when the time comes. Having her sleep with you is up to you, but it won't help her much, if it's truly a night terror, she will have no memory, and therefore no problem going to sleep after.
Good luck!
L.