Changing Maid Of Honor

I had asked a girl at work to be in my wedding, we had a pretty close working relationship. However, I jumped the gun and asked her to be my maid of honor. She has complained about a number of plans that I have intended to make, and insists that I should spend more money on things for guests, which I can`t afford, but won`t lift a finger to help! After discussing it with my fiance, he thinks the bridesmaid that contributes most of the planning and help should be asked. I started thinking that my childhood bestfriend should be, even though she lives miles away and doesn`t have the money to contribute. How to I fix this?!? I really don`t want to hurt my coworkers feelings, but I don`t know anyway to get around it. Who should technically be the maid of honor anyway?