Actually, I think the point of the warehouse is to give Mara just such favorable circumstances. Warehouses are full of stuff. Stuff one can hide behind, stuff one can ambush from, stuff one can drop on the heads of others.
Hence, Mara Assassinates.
Oh wait morals on.
Mara and Jaina are fairly close family members and would never really hurt each other, so it'd turn into a standard sparring match, which probably hands it back to Jaina.