For what it’s worth (I can call myself sort of a bootleg MTG biographer, having written a plurality of her Wikipedia article back in 2021):

• a) Yes, she’s an idiot, but I don’t think that’s why she’s abdicating the seat.
• b) She got into politics in the first place because of Trump. Trump’s 2016 campaign is what motivated her, and between then and 2020, she spent her time e.g. posting white supremacist, Trumpian conspiracy theories on Facebook. Trump was her hero politcally, and she self-admits to not having been politically engaged at all prior to his first campaign. She more or less went into politics to help Trump uproot the “deep state”, and now, probably in her mind, she’s realized that Trump and his MAGA sycophants are the “deep state” – but then so are the Democrats to her. (Edit: I’d add that she was QAnon, which sees/saw Trump as a near-Christlike figure and the only one who could bring the “deep state” to justice.)
• c) I therefore think she’s just fed up with participating in federal politics. She owns (or maybe owned? I never kept up) a CrossFit gym and does have other things to do with her time, and whereas I can tell you she’s sincere and convicted in her beliefs, she’s also totally ostracized from basically every direction, and man, I don’t know what I’d have done in her shoes.
• d) Given the way she entered politics – a populist giving her trivial answers to immensely complicated problems – I can imagine this is just not what she wants to be dealing with. She wants an extreme binary of good and evil where the enemy is simultaneously strong and weak and that her hero is on the cusp of destroying the evil and just needs her help to push him over the finish line. What she’d be doing as an independent is wildly different from what she signed up to do.