Not needed. It would be nice yes, but I rather would have a more diverse selection of demigods.
Sedna can't hold against two players either, and a rook only against weak pushers.
A queen can push harder than sedna, does more damage(or lets others do so) has way way better minions and can rougly imitate sednas heal with shield(though it still sucks).
Queen can push harder than rook(with support), does more damage, has monks/minions and has shield and ofc is more mobile.
Sure she doesnt have a stun(rook roll) or super burst(hammer) but she can still push very hard with spikes+minions. Sedna has silence pounce and heal, but thats it. She has no dmg to speak of save for a weak alpha strike(weak as in not as usefull as bite or pent).