Hey there,
According to our ped. babies can sometimes have a system that works out only 1 BM a week....rare, but it happens.
I think it would be a far worse thing to have the baby wanting for calories than being constipated. Her syatem may need to adjust, but she needs the calories just to be able to make a BM.
Don't stress...it hurts your milk supply, remember that they are amazingly resilient little critters.
Best,
Eden