So I may be a little biased, but in my professional opinion, it is a huge mistake not hiring a planning for the day of your wedding. Sure your best friend volunteered to do it, but don't you want her in the pictures? You don't want to be searching for your mom because she's left to find out why the caterer hasn't arrived yet. And, worst case scenario, if disaster strikes, you don't want to be the person trying to handle it!
The only things you should have to do on your wedding day are get married and live happily ever!