2010 colorado only gets 12-13 mpg

[87fleetsidedude]

It has an inline 5 under the hood, granted it is pretty much only driven in town by my mom to and from her work which is like 5 minutes away. Shouldn't it be getting better than 12-13? any ideas on what the problem could possibly be, I just put a bottle of fuel injector cleaner in it for her and will calculate her mpg after i get back home from college this week. if that doesn't help i have no clue what is wrong with it.

Any help would be greatly appreciated by me and my mom haha

thanks a lot
Justin