My sister has yet again told me I'm watching my nephew, not asked, told. She ask me to come stay the…

My sister has yet again told me I'm watching my nephew, not asked, told. She ask me to come stay the night so they don't have travel at bad hours, and then telling me the day they get here they're going to go visit friends, and I will be watching my nephew. She's so pathetic, she called me this morning asking if it'd go to my mom's house with my daughter help watch my nephew with my grandparents since she couldn't leave her boyfriend, because she'd miss him too much, yet I can't sleep well without my fiance, but she's so far up his butt I'm more than capable of driving two hours to watch 2 kids on my fiance only time off, later tonight she called me asking to go watch him while my mom went to the doctors by where I lived, I would have to leave by 3:30am to be able to get there before they left for the appointment. Yet I'm not allowed to tell her how horrible she is and treats me, and no one else will stand up to her, but when I do get in trouble because "she's sick" she's doing everything to herself and munipulating everything and I just get to be the whipping post.. I've done this my whole life, and I just wish the people who think she's amazing could see how evil she is.