Thesis statement: Kitty isn't as ditzy as she seems--- She's still delirious from the spider bite.
Kitty, as a fictional character, is often utilized when the structure of an episode or scene calls for one character to be "The childish and naive one" or "The gullible one" or sometimes just "The stupid one."
Now, I admit that I don't think Kitty is particularly smart. I don't think any of the characters in this show are particularly smart, really. They're all kind of stupid bumblefucks, which is what makes the show entertaining. So I'm not arguing that she isn't childish or naive, or that she's actually a genius, but I do think there's potential for a reading where something else is the cause for her more extreme ditzy moments.
To reiterate: Kitty is naive, obviously, and not very clever, even before her death. That's just one of her main character traits. Most of the flashbacks illustrate that fact, as well as the journal entries from the companion book.
However, in all the canon material where she's alive, I don't think she really does anything actually all that foolish or downright stupid--- Mostly, she just gives people her trust and the benefit of the doubt when they don't deserve it, and this is framed as being foolishly naive and childish. Which is true. But I'd argue that that doesn't say much about her actual level of intelligence in life, and only that she's way too trusting of others. It's really only after her death that she seems to become the silly ditz we all love so dearly.
Also, all throughout canon, we get many, many indications that you stay "how you died(s)"---
If Julian is still slightly tipsy because he died intoxicated, and Pat's obsessed with food because he died hungry after skipping lunch, and Mary still smells like fire… Then wouldn't it follow that Kitty could still be under the effects of the spider venom and resulting fever she died from, and that as a ghost, she slips in and out of delirium?
Obviously, I know this is more easily explained from a Doyalist perspective by saying "Well, it's a comedy TV show and sometimes you have to slightly flanderize one character's traits to make the episode funnier/more compelling/coherent." And I do agree with that--- That is obviously what's actually happening.
But watching the show while keeping this reading in mind ---that Kitty could at any time slip further into or out of a state of fevered delirium, even in the middle of an interaction--- I think it adds an extra layer of comedy, and also explains a lot of her characterization from a Watsonian perspective that would otherwise only be explained as "It's a comedy! Rule of funny! She's stupid sometimes!"
So yeah, Kitty Parker Higham is… The Amazing Delirious Spider-Woman.