Hi, Julz
I am a new border collie pup owner and haven't encountered this problem yet, but I have kept a good suggestion regarding this for future reference.
Train Dymin to sit whenver she meets someone(you coming in the door from the store, strangers approaching her to pet her...).
It should be simple.
Go outside and come inside in a minute tell her to sit, repeat this plenty. DO this everytime you come home, or someone comes over to visit. Also get a friend to come to you on the street and yard, whatever, and get to sit. She will begin to associate meeting with sit and instead of jumping up on you she will sit.
I reread this and I know this isn't the greatest explaination--in a hurry, can't rewrite it...
Hope this helps!
Carla and Fay