S.G.
Read a very calming story to her "every" night efore she goes to bed. When she wakes up with the terrors, her breathing is also out of control. Try to get her to breath in and out with you. Have her watch you and copy you. Take long breaths which will force her to control her breathing. If you can get her to do this...it will calm her down after only a few minutes. She will start to yawn and then get tired and want to sleep again.
Sounds like someting is bothering her during the day that seems to be cropping up at night. Make sure she feels safe during the day and well cared for. Keeping with a regular routine and scheduled feeding and bedtimes always help.
I'd also check with a doctor if things don't get any better with her being thirsty all the time. Some children do require more liquids during the day than others. It might be OK.