So an issue i see with this is that, her lips and face stretch out towards the dick, when in real life, lips can only follow the jaw, they aren't octopus with omnidirectional articulation. So I think you should make it so that when she thrusts her head forward, the lips stay with the face, or maybe very slightly cave into her head, as the friction with the dick would make them delayed, and then when she moves her head away, the lips should stick to the dick stretch from her face, follow her face while sticking to the dick like it was a magnet.