Aly: From the dog's body's point of view: the length you are doing is probably good -- a little longer would be ok, but with her age, I'd be leery to do more than 3-4 miles several times a week. The hips are still developing, etc. But exercise is key... keep her weight in control now as she is growing, and you will minimize her potential for joint disease as much as you can (the rest is all genetics). Once her bones are older (ie, she's 12-15 mos old) you can build up the running distances for her. Keep the pace fairly easy for her (ie, she's not at a "run", just a jog).
She is adorable -- that is how they get you to keep them!Congrats on the new member of the family! HAVE FUN!!!
Jes