Tbf, whether Mao is a lesbian, whether she dated a very horny female Yuuki (who admitted in a previous chapter that even before changing, they were a "perv"), whether she's now pining for Rinko and thinks that since she has no chance, she's going to support Yuuki x Rinko, whether Yuuki is now a lesbian "trapped in a man's body", whether Rinko is bisexual, a lesbian or it's only because she changed sex that girls give her hard on and she even used Mao as fap material, and finally, whether she's attracted to Yuuki because she's bi or because of Yuuki's has a somewhat feminine appeal and so she's always been unconsciously lesbian...
All of that is pure speculation and the author did a good job of leaving clues but no proofs. The only thing that's sure is that we should wait for them to clarify.