Sailor Moon was fighting Sailor Venus because she was being controlled.

“Just give up Sailor Moon..”

Sailor Moon continues to fight her until Sailor Venus goes behind her and hits Sailor Moon with an a strong attack causing her to hit the floor and detransform back into Usagi.

“Usagi-chan..”

Dark Sailor Venus then headpats her, she still cared about Sailor Moon since Venus is one of her guardians and Venus Teleported to an area with flowers and drops Usagi on the ground.