Her children are semi-mythical. The Moon (Goddess) didn't literally bang a deer to make the first keepers. None have ever addressed her in the familial way the Winter Queen does and a parent-child dynamic is different from a sibling one. Siblings evoke the relatively same level. We know that the Winter Queen is strained by the effort of raising Ysera. Now, you can mention that Elune was already measured in BFA by way of the Leatherworking quests and how all she did was numb the night elves burnt up rather than interfere directly, but both of these are vague enough and don't involve humanizing the character. Both making her be the goddess of more than the night elves and making her sister (whom she's dubious enough of to call Ysera a pet) a prominent character lean towards explaining Elune and making her an active actor rather than a behind the scenes unexplained one.