It had been a long time since I read the first chapter, but going back to it now, Saki was barely concealing her gayness from the start. Wouldn't be surprised if her mom suspected, lol. I'm glad to have a new non-subtext yuri series from Kuzushiro.
I thought it seemed pretty obvious that Saki was gay but I haven’t read any of Kukuzhiro’s other works so I didn’t know if this was just gonna end up like tropical fish with endless baiting.
Rereading chapter 1 it seems heavily implied that Saki’s mom knows she’s gay, or at least suspects it with the way she said “but you were never into piano that much were you?”