Are you sure you're using the right comparisons? A Cocker is a very small dog, probably 15" at the withers at most. An Irish Setter is almost twice that. At 9-10 months, the average Irish Setter puppy should be around 23"-25". Are you SURE you got a very good look at the puppy's size and you're *positive* that it is an Irish Setter?

By the time the IS puppy was 6 months, she should've been 15" already. The fact that she hasn't grown between 6-9 months is very very odd. ETA: Some lines of dogs take a longer time to physically mature (I know some breeds can take upwards of 2-3 years), but they almost always reach their full height by 12-15 months, with very rare exceptions.