It's a bit unusual to go so long between poos this early, I presume she's going ok otherwise? PLenty of wet nappies, weight gain etc? The only thing I can really think of at this age is a bit more milk to get things moving better... it might just be the way she is though.
Breastfed babies do naturally tend to go longer between poos as they get a bit older (usually 2-3 months) - a couple of weeks even! And when they go....they really go.