The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
Irony, Hypocrite, What You Are in the Dark, Hidden Depths, and then it goes to more specific tropes such as Armoured Closet Gay and Suspiciously Specific Denial. Depends on the situation.
Space Battles Dot Com fanworks (unnoficial) index in my Sandbox.I can rule out hypocrisy, since she honestly believes all manner of sexual activity (including holding hands) is perverse. Which is why it surprised her to learn she had a hidden fetish and immediately rejected it. It's also the reason she takes the longest to unlock he Heart Gear's immoral weapon, because she has to accept that part of herself first.
Irony could work, but I feel it's too broad.
Edit: Nevermind, I just remembered Beneath the Mask which fits the situation exactly (excerpt from second paragraph):
Is there a trope for someone with an ambivalent nature?
For example: In Hybrid X Heart Magias Academy Ataraxia, Hayuru's character is strongly against any and all forms of sexual activity because she believes it's immoral. So she's surprised when she finds out that she has a hidden catgirl fetish. Even after being made aware of it, she initially refuses to accept it, because it goes against her personal beliefs about sex.
Edited by MiinU