> That.....frankly doesn't make sense, or it breaks the English language in ways that I'm not familiar with

Correct; it is massively ungrammatical.

> Do you mean that instead of saying "it's her apple" you'd say "it's she apple"?

No possessive form is indicated. But instead of saying "I gave it a dress", you would say "I gave she a dress".

Well, thank you for explaining. I have complete respect for anyone's choices in this area but I'll leave the opinion on this particular choice to myself.

Edit: looking at other comments, it seems like it might not be the correct explanation after all?

As someone else noted, GP is just misunderstanding a frankly confusing subject. There are essentially two common ways for people to specify their pronouns.

Some people desire a single set of pronouns, and indicate this using the nominative/accusative pair (she/her, they/them, ze/zer).

Other people accept either of two different sets of pronouns, and indicate this preference using the two nominative forms separated by a slash (she/they, they/he, and apparently, it/she).

We should introduce that community to the Pipe character so they can disambiguate between the two forms.