Alice didn't see the newborns "leader" because Riley was unknown to her and Victoria, told him not to think about her or make any plans till the last minute........
But why didn't she see Aro sending some of the Vultori, to check on the newborn situation?
How did she miss them meeting up with Victoria?
Then all of a sudden after the battle, Alice and the rest of the Cullen's acted as if they had known all along......Was this just a vision SM left out? Or was Everyone evading Alice's visions, by not making any set plans?