its not important as no intention of showing or breeding but when do pups get their adult height? 
my whippet puppy is now 28 weeks old and 17 inch at the top of shoulder. how tall do you think she will finish up?

She probably won't grow more than an inch or so now, if not over exercised. So that puts her right in the standard. In general most whippets are more or less finished growing upwards by 6/7 months, but so many things can affect height. Your best guideline is the size of her parents, grandparents etc. Is she from show or racing lines? If racing is it ped or non ped? There can be huge differences in whippet sizes.

The best thing you can do to make sure she doesn't get all leggy, and to protect her joints for the future. is to make sure she's not over exercised. Free running is important for growing sighthounds but I also stick to the '5 minutes exercise per month of life' rule. so at 6 months no more than 30 minutes exercise.

> when do pups get their adult height?

It may be dependent on breed, but mine are adult height by 6 months.  They just fill out after that.   (Long Coat Chihuahuas.)

She may not reach her adult height until she is 12 months. It really can vary a lot on several things.
I have been involved with the breed for decades, due to my mother owing the breed since 1963, so I speak from experience