Please note that this is an undeveloped theory, and I would greatly appreciate feedback as well. Here it is: Calla was/is bisexual. I have several reasons for this. First of all, she never mentioned her love life, if she had one. She may have concealed this due to the Elves' discrimination against LGBTQ+ people, for the matchmaking system disregards it. And then to my main point, which I screamed during math class because... y'know. Calla's panakes tree. Think about it. What are the colors? Pink, purple, and blue. The colors of the bi flag. And they shift back and forth, equally in the wind! Okay this is super undeveloped FEEDBACK PLEASE :)
The thing with the tree is very convinsing, however, I'd like to note that the Elves' matchmaking system has nothing to do with the gnomes and that Calla would probably not conceale it within her family. She would also maybe feel more comfortable telling Sophie because she didn't grow up with Elves. I feel like she never felt the need to keep things from Sophie. With this aside, I think your theory is very intersting and a great thought.