J.
Night terrors? It's about the right age, I think. I don't know, but I definitely would do whatever it takes to get her through this. I don't know what your doctor meant by "behavioral," but I wouldn't say it's a sleep training issue - she clearly knows how to sleep on her own. I think if it were me, I'd experiment to see if you can figure out what the trigger is. Does leaving the lights on help? What if you sleep in her room or bring her into your bed? If you can figure out what's bothering her, then you can work on fixing it and getting her back into her own room alone at night.
If she's overtired, that can cause sleep disturbances too. Check the recommended sleep hours for her age and make sure she's getting enough. If not, work on helping her to sleep more during the day. Don't assume that keeping her awake or skipping naps will help with nighttime sleep - what happens is the opposite, and the more tired they are, the more trouble they have sleeping.
It sounds really scary for her and exhausting for you! I wish I had more useful advice, but good luck to you.