He and she in Mandarin looks like this:
Male tā: 他
Female tā: 她
What would a non-binary tā look like? 也?
它 is for animals and inanimate objects, not exactly fitting.
祂 is for gods, not really appropriate.
牠 is the same as 它.
For practicality purposes 你 could work the same:
male nǐ: 你
female nǐ: 妳
non-binary nǐ: 尔?