I think this is surprisingly common. I used to tell Mrs. E she gives amazing head and she'd dismiss it, on the theory that men enjoy getting head from anyone and nobody would ever say it was bad. She was actually pretty shy about it, and also considered it very intimate.
She knew I liked watching her, but it took quite a bit for it to really click that she's skilled and looks good doing it, and that it's something she can do confidently as a way to perform, both for me and for play partners. Once she got into it she had a little game going for a while, which she'd jokingly call "eye doctor", comparing different licks and strokes and asking which one felt and looked better from my perspective.
That realization that it's not just a sex act that happens to use her mouth, but a way for her to express something fun and playful and enjoy very positive, joyful attention.