Motive is what we need to establish so we can delve deeper. I can offer some suggestions...
1) Early symptoms of megalomania: she's president of Birdiebee now, according to Total Divas. She cooperates a wine brand with her sister, plus she's an active wrestler, making her feel all powerful, so stiff kicks are a way of discharging what she feels is the great power she now has because of all she does in life. If others get hurt, it's by accident, because this trip she's on is for the betterment of all and she can't be stopped now. Brie's on fire and the world needs to burn.
2) Anger management: Brie's gotten hot under the collar. Something in her life's caused her to go off the deep end, a feud, a bad experience, or something internal to her. Lana and she might have had bad words before the incident, at, or away from work. I think it could be either, or neither. Brie might have gotten mad for other reasons, bottled it in and released it in a big burst. She did say in an interview that this does happen if she represses her anger.