Aside from her being obsessed the malicious ghosts have talked about being seen/wondering if she has seen her and there's not any real evidence of ghosts trying to hurt people who can't see them directly, in fact how much they can hurt humans directly is kind of in the dark considering mieruko can normally walk through them but they certainly have tried to attack her when they noticed she was aware of them.

I'd say that from what we know we have to assume that theres some weird rule there that AT LEAST pisses malicious ghosts off and that the main other possibility is some asspull of a misdirection by the author.

I'd be curious to hear if you have a different take that explains the story better though, I might be have missed some other way of looking at it.