I guess I suggest that letting her have her time. Don't lie...that's just mean. I remember I was afraid of roller coasters and I went the first time to SFMM when I was like 8 or 10 and my brothers forced me to ride Revolution. Hated it! I think when I was about the same age, I went on Big Thunder with my oldest brother, it's on videotape...and you can see how badly I behaved. My brother couldn't get the camera up past the little warning label in the train because I was holding his arm very tightly. I think Splash would be the easiest to try first. Yes, there is that drop, but it's just one drop...the other drops are minor and your sister will have the characters, music, and storyline to get distracted by. You could try bribing her. Ice cream tradeoff sounds great, so does "you ride this, and you'll get to pick the rest of the rides...".