"I think it's more likely that said coworker was just annoyed with me because I was seeking reassurance that she wasn't mad (because she sounded mad on Microsoft Teams but it is hard to tell with written out messages and I'm crap at deciphering how someone is anyway). Said coworker did not want to give reassurance, and okay, that's not her job, but I had asked her to be gentle with me this week because of my friend's death, so it wouldn't have killed her to be nice to me. "

I may be of no use here because I am not good with reassurance to others - I usually think I am being nice by not engaging with someone but I am a tad misanthropic and to me being left alone is the best thing anyone can do for me. But anyway -it might be something as simple as a difference in what a person thinks makes something nice or not nice in a work situation.