I'm deciding what to with my girlfriend, since she is my subordinate
Why do you think of her that way?
I am the dom, I get to decide.
It's not wise to have a romantic relationship with one of your subordinates at work, since this can be looked down upon by others who think that you are abusing your power.  And if you don't work with your girlfriend, then it is even worse for you to treat her as inferior.
wtf
There is a weird power dynamic that might get you both fired. If she gets unhappy you could be fired. Please rethink your relationship.