She loves him for many reasons. A beautiful love story no doubt. But she is a realist and knows what he really is. An incorruptible purist. He'll kill to protect that which is sacred to him without hesitation. A side effect of his autism and high IQ. She loves him for that too. She also needs his resolve and singular strength of heart to beat the AI.
His autism gives his mind a pattern of thought the AI can not make an algorithm for. A connection and understanding of nature and animals that makes him the anti-thesis of the AI. Yet, oddly similar in his ability to focus on one thing and destroy anything that gets in his way to protect it. The AI's natural enemy in the universe and she found him and is in love with him.

Now she must use him. His trust in her is unshakeable. His loyalty and love that of an animals. A monolith trust. She must use it against him to save the world. If he dies she will kill herself for it. He is just a child in so many ways. She is the demon who must use his purity as a weapon to cleanse the world. If he knew how she was going to use him it would destroy him. He would devolve into madness and a bottomless pit of depression. He would shrivel up and die. His love and trust for her is one of a kind. If he found she used him he would shatter and die. A child dying from a broken heart.