Frogga,
Your sister sounds horrible. Self centered and completely involved with only herself. Of course, you could "accidentally" spill some slippery stuff on the floor then ask her for something. If she should slip and hurt her butt...Oh well, maybe some pain is needed. Of course, I never recommend anything like this, but you know..loll. One can daydream. Just keep in mind that her being your sister is only a biological accident. You never got to fill out an application as to the type of sister you would like. You know the saying..what goes around comes around. Hope you mum gets home soon.
Mary