Wasn't it Thancred who refered to F'lhaminn as 'Lhammin'? The two were very close due to the events of 1.0's Ul'dah storyline so it makes sense he would (he refered to her even then as the "famed Songstress of Ul'dah" and "that flowers really do bloom in the desert" in reference to her, showing he really did feel strongly for her, although in his case it was probably just his flirting talking).

Also in Y'shtola's last scene in 2.55 (when she cast Flow), didn't she say "Farewell, Mhitra", showing cracks in her stoic facade that her sister is obviously close to her in her heart? (I'm too lazy to check my screenshots to verify this ).