This morning I beat Betty! Yay! It only took two attempts this morning, where the first was more of a wake up run.
What I found to work best for me, an entirely non-boss-fight style gamer, was to run around near the edge of the arena when Betty is in the Roll Phase. It doesn’t matter what direction as long as you keep moving in the same direction. This should place you at a safe distance always. When she’s done with the third roll I could strike for a couple hits. Then I’d return to distance for a few upgraded flame attacks. I only lost 1 pip of health this way. I don’t doubt that it’s possible to use this approach for a hitless victory.