The way Jack watches her is like she's air, like if he doesn't breathe her in he'll collapse. He'll trip just to touch her skin on the way down, ask her advice when he already knows the answer so he can watch her lips dance. It's his way of saying he needs her, these pratfalls and inhalations and humbling inquiries. She imagines that if they had known each other when he was that brilliant ER surgeon, he would have had her brought into the room and asked her how to best fix the seemingly inescapable paralysis that threatened his future divorce.
But this is not enough for Kate.
The way Juliet watches her is like she's a curiosity, like if Juliet doesn't study her enough Kate could turn out to be an unseen danger. Juliet walks with her head high, never asks for advice because at this point, Juliet only wants the answers from someone she trusts, and the only person she trusts is herself. It's Juliet's way of saying she doesn't need anyone, and she breathes when no one is watching because needing air could be construed as a weakness. Kate imagines if they had known each other when Juliet was delivering babies to mothers that lived, Juliet would have evicted her from the room and shut the door.
And this has to be enough for Kate.