Elea never admits to exploring Neverwhere, dude. Quite the opposite.
Medb still tries to trick and deceive MC. even if it is because she is interested in him and does it playfully, it's still not trustworthy at all.
"I love mythology....spent a lot of my free time on research.
...love exploring unknown, unraveling puzzles, and deciphering hidden meanings.
...can't get away from the stories about ancient gods. Or the illuminati and freemasons...
...people usually tell me I'm chasing fairy tales...
My dad and I were actually always of one mind. He always supported me. Except in this case. He absolutely hated it."
On its own, that could just be hobby. Cute but harmless.
In game context, above is literally her about to end up learning about Neverwhere.
So you are correct, my wording was wrong, she never says she's researching Neverwhere.
But while she never names it directly, above is basically "Do you encourage this girl to learn more, effectively putting her in danger, or tell her to drop her hobby?".
I don't see how above can end up anything else but her learning about about Neverwhere.
Medb absolutely tries to trick MC. But guess which choices give affection points with her? Not being an idiot ones.
She offers deals and honors them. Changing deals because you got greedy? Oh, Elves will absolutely scam the shit out of you.
But on surface? Deal is a deal. Don't change it on the fly and you're good.
Way more trustworthy than any Templar shown so far. Yes, that includes mommy dear. Lying bitch...