The formula is not for her house it is for the baby, does she not understand that? Also premixed formula does expire, does she plan on giving it to him after it expires since it may be a long time before she can have the baby at her house again? Obviously she doesn't know the difference between loving a child and spoiling one, and baby's do tend to get a little on the fat side when they are properly nurished and cared for.
Her attitude about being stuck in a car for 45 minutes to get to a parenting class, shows that the baby doesn't mean as much to her as she does to herself. Without taking the parenting class she may never get unsupervised visitation. Just keep a log of when you have offered her visits outside of what the court ordered and if and when she does see him, the courts will definately be able to see that she is the one not doing what she can to see the baby, and follow the CO, not you and DH.
She truly is in a idiot and mental case. You and DH keep up the good work and keep loving the baby like you do, he will be the one to benefit from a loving and nurturing family, and will be thankful that ya'll fought hard for his safety and wellbeing.