I completely understand your point, and I have many trans friends that do NOT vibe with the term 'trap' because I agree with the OP that it implies that they're deceiving people of their true identity. They'd use it jokingly amongst each other but they would not want to be actually labelled as such by others. And that's not to invalidate those who are fine with the 'trap' term.
If we're just looking at Quinni as a character, I made her canonically trans. Never in the dialogue do I use the word 'trap' once except in the options menu when I allow the player to choose her genitals. And if I’m being frank, I only did that because it’s the commonplace H-game terminology — which is why terms like “futa”, "femboy" and “trap” appear on the page as shorthand genre descriptors. So I felt omitting one mention of the word in the actual game was worth avoiding offence.
By setting the options to "has a penis (intended)" and "has a strap-on/vagina (alternative)", it leaves her label open for anyone to self-insert what they like to view her as most. You are free to label her as a 'trap' if you so wish just like how you can choose for her to be a cis girl with a vagina if you so wish, the dialogue does not change a single bit with that decision. I've previously encouraged anyone who questioned Quinni's identity by telling them that she's whatever they want her to be and that's okay.
And you’re absolutely right — I shouldn’t let one person dictate how I dev the game but I’ve turned down plenty of requests before. This time, it just happened to be something I genuinely agreed with and had the power to change. People can disagree, and that’s fine — I’ll always make the calls that feel right to me. I just make games that I wish existed and I'm just glad people enjoy it too.