najimi from komi can't communicate is explicitly non-binary.
other than that, i don't have any shows to recommend, unfortunately. non-binary and gnc individuals are sorely underrepresented in anime and manga
i would like to say though: as a trans woman, it makes me really happy to hear the support your coworker has for their child. a proper support network is crucial for any child, but this is especially true for trans children, so thank you to both of you!
She's an absolutely incredible mother and supports her child in everything, it's really lovely to see how hard she's trying to show her child her support. I think if her child can also see characters they relate to in media that would be a massive thing for them.
I'd forgotten about Najimi! Komi-san would probably be a good show to recommend to them even regardless of Najimi since it's so good, but that's a really good suggestion, thank you!