Depressing pool, maybe? The tiny Marisa ornament on her cake seems to solidify that absolute despair that is lonely Alice. Even Shanghai looks sad for her.
Poor Alice how can Marisa stand her up on Christmas. Marisa is probably at the SDM's party and mostly to steal expensive gifts. Reimu's probably there too for the food.
Eh, it doesn't really feel like it to me, since she actually looks angry in this one. The other birthday Alice posts, where she looks happy, are the depressing ones.