[@Kirah] - Hmm I'm not totally sure on that. If Natasha is only hiding via single sense, aka eyesight and is essentially invisible, I'd imagine Niah would easily hear her breathing/heart beat. If Natasha is focusing on multiple senses, it would only last for a super short period of time as is, and likely wouldn't go exactly noticed by Niah. But the "depression" area would make sense, since there are more than the 5 basic senses, and odds are those are strengthened in Niah even if she doesn't realize it/actively use them. So perhaps she'd get weird vibes and such when near Natasha when fully hidden. 

But I'm open to interpretation :P