I had that problem All.The.Time. with regular disposible diapers. My daughter was the same way, when she went she WENT! I had her in a bumbo one day and poop was just EVERYWHERE! So I switched to cloth. I had heard that they did a great job of containing the flow so I gave them a shot. I figured that I was washing poop anyways right. But I tell you what, I absolutely never looked back. I even had my babysitter converted. She was over here one day and my daughter had one of those over-flowing breast-fed baby poops (that would have been everywhere had she not been wearing a cloth diaper) and she changed her but put her in one of the few disposibles I had left. Not more than 30 minutes later, she went again and instead of it being contained it was everywhere!
My daughter is tiny so before I switched I would just put her in the next size up. She was not even 12 lbs when I moved her into a size 3 in a vain attempt to contain the poo. No disposible I tried worked as well at containing it as cloth does.
I know cloth is not for everyone but its not as big of a deal as everyone thinks it is. For the breast-fed only poo you dont even need to rinse or anything. Just throw it in the washer, soak, hot water wash and rinse until you have no bubbles. Put in the dryer and you're done.
I converted while my husband was deployed and he came home and saw how well they worked and has become a total convert too.
If you are interested to look into cloth, here is a great link for you.
www.babycottonbottoms.com
This is where I got all of my diapers and accessories.
HTH