This response is provided based on the information you shared and should not be used as the sole source for making a decision. You should seek guidance from the chain of command, IG, JAG or other certified agencies before making any decisions. How you chose to use this information is totally up to you and is your sole responsibility.
Based on the guidance in AR 600-20 there is nothing that prevents a Soldier from deploying if the postpartum deployment deferment period has been met. Therefore I believe the Soldier is eligible for deployment with the ability to discard the milk if there is no reasonable way of getting it to the baby.