This is one of several peculiarities of the Standard Kits that I found while working on my general replacement of Inform’s pronoun handling.
If you’re using Inform7’s v10 and up, try using “Non-binary Pronouns by Sadie de Might”.
I’m still slowly providing updates, first to finish documenting what it does, and then next to make sure it works with v9 and Z-machine (which it doesn’t yet).