Where is she meditating? Is this spirit inside her home? Can you ever said anything to it when its in her? Has it responded?
It seems silly to only happen when she meditates... I wonder if its just been around her for a while. Does anyone else live with her? Does she have any animals?
Weird questions I know but it will effect the ways in which you cleanse the home since it sounds like if she can get rid of it from her house, then she wouldn't need to worry about it possessing her.