AITJ for telling my coworker I won't swap desks with her because she "needs" the window seat for her mental health

I work in a medium sized open plan office, about 40 people on our floor. Desks are not formally assigned but there's an unspoken understanding that people have their regular spots. I have sat at the same desk near the window for about two years. I like it because of the natural light and because it's slightly away from the main walkway so it's a bit quieter. I got there first, I kept showing up, it became my spot.

Three weeks ago a coworker I'll call Petra transferred to our floor from a different department. She's perfectly nice. On her second day she came over and asked if I would be willing to swap desks with her, pointing at mine. She explained that she has seasonal affective disorder and that natural light is really important for her wellbeing and that the window seat would make a significant difference to how she feels at work. I felt genuinely bad about this because I don't want to dismiss something that sounds real and difficult. I asked if there were other window desks available. She said mine was the best one. I said I was sorry but I had been at this desk for two years and I wasn't really comfortable giving it up.

She seemed surprised and a little hurt. Since then she has mentioned it twice more in passing, once saying she "thought I was the kind of person who would understand" which I found a bit manipulative honestly. I haven't moved. But I'm now second guessing myself because I know SAD is a real condition and maybe I'm being selfish about a desk. AITJ?

TL;DR coworker asked me to give up my window desk of two years because of her SAD diagnosis, I said no, she's brought it up multiple times since and implied I lack empathy, wondering if I handled it wrong.