WMG / Tari Tari

Naoko, the vice president, was in love with Wakana's mother, Mahiru

The way Naoko responds to Mahiru during flashbacks it very telling, and she clearly had a hard time dealing with Mahiru's death herself, which is evidenced by her visions from the past in which she sees Mahiru call out to her. Naoko doesn't seem to be married in any case, so she could be lesbian. In any case, she went to great lengths to maintain the choir club that Mahiru established. Having to deal with Wakana, who looks so much like her mother, probably opened up old wounds for her, which puts Naoko's actions in a somewhat different light.