The books:
Have A New Kid By Friday by Leman
The book series by American Girl books... has topics/books on feelings and friends... you can read about it on Amazon. Just input "American Girl books" in the search bar. Its for girls this age.
Also, the "Tween" age is coming up.... 9-12 years old is the Tween ages. And at this age... its sort of a cusp age... my daughter is 8... and she and her friends are more 'emotional' lately.... changing cognition/hormones/feelings....
But, she needs boundaries... and for the adults to be consistent/firm with her.
Also, they need "bonding" too, still at this age. With Mom etc. At certain ages, it is still real important.... and is manifested differently per age.
My Daughter for example, when she gets all hissy-fitty... it is actually when she needs 'Me'... and to bond with me... amongst everything else.
Tell her she is 8... not a baby.
Sit down.. have a MEETING with her... talk, lay down rules, let her express herself too for any issues.... make it a 2-way street... but let her know, MIStreating people/family... is a BIG no no.
Give her chores.
Make her responsible.... as well, for being IN the family. Tell her, she is a PART of the family.... and she needs to learn that.
Does she have problems at school?
With friends?
School work problems?
See what 'problems' she has or concerns...
Often, insecure people/kids... try to act all "big"... but they are not and are actually vulnerable/insecure.... inside.
Tell her you will NOT argue with her.
Sign her up for classes maybe. Marital arts, Karate etc.