In the American regionalism "Put 'er there, pardner!" why is the hand a she?

In the American regionalism

Put 'er there, pardner! (i.e. Let's shake hands)

why 'er ?

P.S. When someone is manipulating equipment, such as a crane or a hoist, to move a heavy load, someone directing operations might yell the command "Put 'er down! Put 'er down!" if he notices that the load has become imbalanced. Or he might be motioning the crane operator to keep moving in a certain direction, and then say, "OK. Put 'er there."

Are these two uses related?

Solution 1:

Since 'her' is referring to the hand, the French word for hand is 'la main' which is feminine gender. To shake hands in Spanish is "... la mano" (feminine). I don't know if your phrase is derived from these, but the gender fits and the West was once owned by either the French or Spanish.