So after reading through the chapter twice, I just realized that Julia never let Romm know she could see smaller spirits.
As far as he knows, she's just a girl who "thought he was a fraud, but is glad he's actually real" after almost falling to her death after being warned. She never mentioned that she could see spirits (not that he would necessarily believe her given the kind of hacks who show up to his testing sessions).
Would be interesting to know if his reaction would have been different had he realized she was a medium (albeit a relatively weak one). Although she might be as strong as Mitsue used to be as a child, since it was only recently that she could even sort of see the strong ones (Romm was surprised when she was able to see the strong one in the alleyway a few chapters back).
@mokonaarappa
I think he can see the smaller spirits just fine. He's just more focused on the stronger spirits during the tour because he's testing his items on them.
That's why Julia thinks he's a fraud. She can't see the strong spirits that's he's using for testing purposes.