My girl is temperamental as well, but I don't find her that stubborn. Before you call your girl stubborn are you sure she understands what you want? If you say "sit" and she doesn't listen it's likely she doesn't understand what "sit" means...especially at 15 weeks.She is wonderful albeit very very temperamental and stubborn
I suggest you read the book "The Power of Positive Dog Training" by Pat Miller. It is a FABULOUS book that really taught me a lot about how to train Snickers. You can pick up from Amazon here under $15 and they have used copies for under $10.i will be looking for tips and tricks on training.
Also, get yourself a clicker and start to clicker train Missy. It is really easy once you realize the click is a marker and is used to mark a behavior and not elicit a behavior. For example, a click means "good girl here is a treat" and NOT "sit". Make sure you "charge" the clicker first. I can't access YouTube from here, but there are some real good videos by "The Amazing Dog Training Man" on how to do clicker training.
If you get Animal Planet watch It's Me or the Dog.
The key is never scold, be patient, and be consistent. There are several sources for potty training on the web and you would train Missy the same way it just takes a bit longer. Give her treats when she eliminates outside and if she has an accident in the house hit yourself (it's your fault, nit hers) in the head with the newspaper and silently clean up the mess.Especially potty training and unwanted nipping, she really seems to like nipping my children and it is a habit that i would love to break but i am struggling greatly with this and potty training :-(
House Training How Tos
House Training Your Puppy by Perfect Paws Dog and Puppy Training
Puppy House Training