Sadie's litter mates all had the typical catahoula leopard stripes. She was the only one with the rottie markings. You're right though, she really doesn't look like a rottie. She has much longer fur than her siblings do as well. The vet at the shelter said that she will probably only get to about 50 lbs max. Really small for a rottie imo.
Sadie's nose also doesn't look very rottie-like. She looks like she is a very sweet-natured dog and she will be a great addition to your family!