1 to 2 pounds a week at 9 months old, seems like alot to me. From my experience, pups tend to slow down around that age and maybe gain a lb every couple of weeks. My latest pup is 17 mons old, 22 inches and has been sitting at 53 lbs for several months. His body is still changing, but he's not been putting on much weight since about 10 months old.
Dad sounds like a BIG boy! 22 inches is a bit shorter than the standard - the recommended standard starts at 23 inches for boxers, according to the ABC and AKC. And at 70lbs, he sounds HUGE! Just thinking of my pup at 22 inches and having an extra 20 inches added to him - would be ALOT of stress on his joints and bones. LOL - actually trying to picture my Bauer with all the extra weight kinda makes me giggle - you have to know Bauer to understand. lol
If she's gaining that rapidly, I'd wonder if she's getting too much food?? Some boxers are bigger than others, and some smaller than others - but to me, she's gaining weight too fast and should be slowing down. Boxers grow up the first year and out the 2nd year, so I wonder if she's not eating too much? Just a thought. Structure will play a lot to it, but genetics is also a factor. Really hard to tell what size they'll be when they get older....til they get older.