Start with Nitro, pay her money if you have to. Then, everything else will be easy. Tell her she won't die and say thousands of people go on it every day and come of safe, so she will too. I did this at Knott's with my coasterphobic friend and Supreme Scream...Boomerang, Montezumma's Revenge, and Ghostrider were cake for him after that...
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Life is like a coaster---
You go up, down, turn-around, and upside-down...and then there's all that pressure on your head, too...