Same applies to homogenized milk - if parent wants to continue sending fine. But bottles come prepared not done by you. At this age child would be having it poured into a cup and not warmed. There is no reason to sterilize anything - I mean you don't sterilize her spoons and plates so why the bottles.

Sounds more like the issue of speaking with mom that it is time to let the child grow up. Mom is holding onto the past - child is not a baby and does not deserve to be treated like one.