but can't find it...
I am 5'5" and weigh 330. I weighed 10 lbs more last year, and I went on AK Safari, Soarin, RRC, Splash Mountain, Test Track, Space Mountain, Kali River Rapids, Pirates, HM, Pooh, Snow White, Peter Pan, IASW, BTMRR, TofT to name a few.
Don't know what your sister's specs are, but if they are anything like mine, she might be a little snug in some of the rides, but will be fine. I ALWAYS ask a CM before getting on a ride, as they know which cars might be slightly more accomodating.
allears.net will be very helpful.
Hope your trip is fabulous!