Firstly, Bettie had good energy and enjoyed herself. She looked great in photos because she was happy when they were taken. Bettie said herself that her happiest moments were when she was being photographed outside, perhaps playing on the beach. Beauty is in the eye of the beholder, but anybody will glow when they're feeling happy and carefree.
Secondly, Bettie took care of herself and took steps to protect her beauty. She worked out in a gym every day and walked all over New York. Bettie loved being outside, so she slathered herself in baby oil and lay in the sun to achieve a smooth, healthy tan (nowadays you're better off slathering yourself in sunscreen! Bettie spent gobs of time in the sun, yet never wrinkled. Even today in old age, her skin looks fantastic. I have no idea how she pulled it off). Bettie also always ate in moderation. She didn't smoke and rarely drank.
Thirdly, Bettie knew how to look good. She found a hairstyle that not only flattered her, but which distinguished her from other models. She never caked her face with makeup, but artfully applied mascara, liner, and true red lipstick. These were enough to accentuate her features, not disguise them. When she was barefoot, she made a point of always walking on her tippy toes to give the illusion of heels. Bettie, who wasn't very tall, knew this elongated her body. It also made her more graceful. Another way in which Bettie disciplined herself was by being perpetually aware of her body and her face. Bunny Yeager, the famous pinup photographer, remembered that she only caught one photo of Bettie where she wasn't posing, despite having taken hundreds upon hundreds. Bettie always knew where the camera was (much like Marilyn Monroe).
These are only a few of the things that made Bettie Page so inspiring and beautiful!