Young gundogs are often a bit 'mouthy'
How are you responding to her when she does bite and nip? My Lab was VERY mouthy when I adopted him, it was constant. I found that consistency was key: every single time your dog puts his teeth in anyone's skin, you should say a firm 'no' OR yelp AND turn your back, or walk away for a few minutes.
You all have to be on the same page with this; it's no good one of you doing it if the rest of the family don't.
Also: I agree with you about being careful how much exercise your puppy gets. Goldens, like Labs, are very prone to hip dysplasia, so follow your vet's advice on this. However - there is no limit to how much MENTAL stimulation your pup can have!
Look online and you'll find lots of fun training games and exercises. Not only will it tire your pup out, and thus keep her calmer, but you'll also find it will increase the bond between you
Best of luck and remember, six months is still very young
RE FOOD:
Might definitely be an idea to try something else, especially if you noticed a difference when she was on something else. My Lab had constant itchy ears until I put him on a wet food (Wainwrights trays).