I wonder if the real reason she doesn't let information about her ability be known is because it's the same as Mikagami's, and since it's a skill seen as useless she's actually afraid of being treated as an inferior being, if that's the case this reason can even be used by the MC to make her let her guard down

It's a skill collector type this time. If it's impossible to get more than 5 skills naturally even for the best level of humans, it's kinda obvious she's getting them from something else, like items. Lots and lots of combined disposable items.