answer:It’s a social bonding behavior, called “allogrooming”. Many animals allogroom, and the head is a common target because it’s a difficult spot for animals to groom by themselves. She rubs her head against yours to mingle your scents; she wants some of that lovely conditioner smell to carry with her as a reminder of of you, and she’s leaving a hint of her lovely aroma behind in exchange. It’s the ultimate kitty compliment. I once had a cat that went for my armpits whenever she could. It was excruciatingly painful, bt she enjoyed it so much that I’d endure it as long as I could.