For me when I feel like that I find it helpful to minimize sensory input as much as possible. So quiet, less light, and being wrapped up in blankets with as many comfort items as possible. Snuggling with animals. Not having to be forced to communicate and keeping interaction and decision making very simple (think yes/no only so you can easily just nod or shake your head). I have been told by friends before that they have had to take my keys to my car and do things like that to make sure I stay put.
Everyone is different though. Do you know what she finds comforting? Does she have a special stuffed animal or blanket? Does she like fairy lights? Anything of that nature can be helpful.