Have you talked to the vet about any physical causes for this? Sounds like your puppy is very submissive. Do you ever scold her for peeing in the house? Perhaps you shouldn't even say "no" but use high praise outside.

Check thru all the past behavior threads cause there are a lot of suggestions on how to be a good pack leader so your dog feels secure (which would hopefully reduce the nervous peeing).

It's been a long time since I've dealt with puppy issues since my dog is 10 but I've always lived in an apartment so I know how difficult it can be, good luck!