Some mothers kill their children. Some fathers too.
Yes, there is a love which is stronger than maternal instinct. Instinct is instinct. It is not love, per se. It is instinct, kindness, obligation, it is right.
A love that is stronger than an instinct, is a person loving another person, for no reason than love. They are not their child, not family, they have no obligation, they don't have to. Yet they do. Love is a choice, love is action.
A person who loves his/her neighbour as much as he loves himself, that is strong love. A man who loves a woman who does not repay his love. A soldier who loves his country and is willing to die for his countrymen, loves much stronger than a parent who will not risk much for their children.
Perhaps Phillip is not a woman. But one of his children were deliberately murdered in the womb.
Love and instinct are distinct. They have correlations, but they are not the same.