Whether or not someone is an abusive troll has no bearing on the respectful use of pronouns. I have two concerns here: ensuring people are respected and not encouraging the trolls. If either or both individuals here are trolling, they're getting exactly what they want with our collective response.

In response, I made a process guide for online encounters like these. It works regardless of the other party's motives and better frustrates trolls. If you have the mental/emotional bandwidth, let me know what you think.

Step 1: Treat everyone with respect, including respecting their communication preferences. If it becomes obvious they're not being serious and/or respectful themselves (ball/sack, dog/shit), then simply disengage and report. Their bad behavior doesn't justify anyone else's bad behavior in response, especially because that's what trolls want.

Step 2: If there's only suspicion their requests/preferences are somehow a form of trolling, harassment, or the like, either...
2.1: Respectfully ask non-accusatory questions for clarification, then return to step 1
Or
2.2: Disengage, report to a mod, and let them handle this shit

Rinse and repeat.

There are two overwhelmingly likely results to this little workflow.

A troll is treated with kindness and respect until it's found they're trolling, after which engagement ceases and mods have to deal with their shit. Remember: trolls get off on watching other people's outrage. No response = no outrage = an unsatisfying trolling session.
Someone who is not trolling but is having a difficult time being understood is treated with kindness and respect.