Sorry cannot input Chinese. I feel urged to speak for your girl, since all
her behavioral problems link to one thing: lack of security. Somehow she
does not feel beloved, not secure, not contented, that is why she is "
difficult".
Don't be too harsh to her. You need to let her feel secure first, then you
can reason with her. Treat her fairly with brother, but give her special
attention. For example, celebrate her growth, give her "mother-daughter"
special time if she does anything nice to the brother. Be consistent and she
will change.