Femradiel's plan relied on the effect of the hammer from the very beginning. While she didn't know everything about Aphrodite's powers, she knew when she would have the best moment to attack her… it was when she was at her strongest point… when she uses Self replication. Just like the fact that all the replicas can use and have their own invisible shields and spears, and just like the fact that the exhaustion of all replicas is transferred to the original in the end, their damage is also sent to the original. So, Aphrodite received the damage that knocked down all fifteen copies.