Rottie size varies so much now, too, that it's just a shot in the dark without knowing how big the parents are. But, considering she's put on 10 pounds in the past month, and it's safe to say that she may very well put on another 10 pounds in the next 4-6 weeks, then her growth rate should start to taper off some; a 70 - 85 pound dog would be my guesstimate.
Of course, there are all sorts of variables, like what kind of nutrition she's getting.
And, of course, we could all be wrong . . .