Tantrums, Mouthy, Talking Back

My daughter is 8 years old. I would say she has always been a "perfectionist" in school and she is hard on herself when she does not do everything right. She has a loving family at home, but in the past three months, she has begun to talk back, argue, tantrum and threaten to run away.

She perceives her family as not showing her attention and her younger sister as receiving most of the attention. I know that by saying these things and arguing, it is filling some capacity for control and power, but it is getting to the point that it is almost unbearable.

Please help.