Diva Drama Queen versus the bicycle

We had a brilliant plan. The kids were going to learn how to ride their bikes this summer. Yup. It started with brand new bikes for Christmas. And ended with a "family bikeride" gone awry. It's been a LONG journey. We've been pushing Diva Drama Queen to learn for years. She's 8. The bikes we bought them for Christmas are still too big for them. I suppose I thought they were bigger than they really are? Or maybe it was the fact that the next size up at the store was THAT size. There was tiny and 20". Their small bikes were so SMALL for them I thought the size would be right. So we ended up teaching them to ride on their small bikes. You know, the 12" toddler bikes. We just took the training wheels off. They'll just have brand new bigger bikes for when they get bigger. No biggie. We took them to the stake center parking lot and gave them a good shove and told them to pedal like mad. And little boy blue did great! First try and he was off. And he hasn't stopped. He's awesome. With a little prodding and pushing, Miss Diva Drama Queen got mad and decided that she was going to do it to, she wasn't being shown up by brother. So she did too. We found a better sized bike for the girly, and are looking for one for boy blue. We've taken them around a few places and they've been practicing. They both CAN ride just fine now. And I emphasize the CAN. Little boy blue is a pro now. No problem. Diva Drama Queen is a different story. I swear she is doing it for attention. She knows how to ride. She knows how to steer. She can do it on her own, no problem. But she won't. So when I tried to get her to come ride with the family yesterday, she wouldn't. She threw a giant fit in the middle of the street. She balled. She threw the bike down. She acted like the bike was a scooter. She was in short, a diva. Has been, is, and always will be. And I hate it. No, I loathe it. Yup. Nothing makes me angrier than dealing with a diva. And she's only 8. Grumble grumble..... Anyone else have a diva? Any ideas on how to get her to ride her bike without hating it and me?