Is there any way to help control my niece's emotions and ask her family members to treat her right?

My niece is going through puberty right now and her emotions are like a roller coaster. I can see she is struggling to handle them. My sister and nephew (my niece's little brother) seems to be the source because my sister treats her unfairly and my nephew constantly annoys her. Is there any way to help her control her emotions and tell her family members to just stop doing that? (Please no "Just sit down and talk to them." remedies, they rarely work! I need instant results for her. I love her more than anything in the world!)

Ask your sister to consider allowing her to live with you. If "Just sit down and talk to them" is not an option, that's about all that's left short of a family feud.