Will my dogs fight for dominance ?

i have a lab who will be 5 in september. im going 2marrow to check out a litter of pitbulls , theres only girls left i believe and iv been looking into getting a pitbull for awhile now , but now im worried if i get a girl when it grows up is it gunna fight for dominance ? . my dog does greaat with other dogs but i dont think shes ever been around a female dog , but im thinking if it grows up around her theyll be ok. what do u thinkk ?