I'm not a mother but my oldest niece had night terrors at that age too, I used to babysit her a lot during that stage and it is really scary to see them so unsettled but they're really not in pain and most likely wont remember it in the morning. You can't really do anything to make it go away but if she settles herself that's a good sign. When my niece experienced it I mainly just tried to let her know I was there, I didn't pick her up or anything so she wouldn't get too confused or uncomfortable but I would hold her and and tell her I was there in a calm voice. She still has night terrors rarely, maybe twice a year, it's worse when they're older.
The last time she had one she said there was too many monsters inside her, I was terrified.