I think Alice has some great ideas. I just wanted to tell you about myself. I never had terrors but I've always been a highly imaginative dreamer. Unfortunately a lot of the time they were nightmares and drove both my parents and myself crazy. I would wake up screaming all the time, wouldn't want to go back to sleep, etc. To this day I still dream like this. I have probably anywhere from 1 to 6 nightmares a week. In particular about the apocalypse, zombies, snakes and frogs (who knows why about the frogs). I've completely cut myself off of scary movies. I used to love them but after having my son, I just can't tolerate them the same and obviously I think they're good to avoid for my psyche. However, I'm also good at writing and am just an imaginative person overall. So don't necessarily think it's all bad because it's not. She just has a very active little mind. You have to keep her mind from focusing on things that may reflect negatively in her dreams (completely impossible to avoid it all together but just do your best). For instance, my mom stopped allowing me to watch Scooby Doo when I was a kid. Although all the monsters were fake, they were still monsters. So pay attention to those things. Like going back to what you said about her dreaming you gave her away. Maybe she watched something that got this into her head. Even if the overall message is positive about something, a harmless movie about adoption could plant the seed. Mix in a creative imagination and presto, she dreamed it happened to her.
And stress can bring on bad dreams. If she started pre-school that could be a possibility. And all of this could just be short lived anyway. Best wishes to you and your little girl. You may just have a very create child on your hands which is nothing but a great thing!