Excitment peeing can turn into submissive urination, which takes place in older dogs who usually who've been yelled at or worse for peeing in the wrong spot. Fourteen weeks is young, and they can't hold it very long. If you leave her out of the pen a pad should always be close by. My breeder told me to praise the success and ignore the mistakes. Have lots of Natures Micacle around and use it to clean up mistakes so that she won't be tempted to return to the spot. Here's more information, the good news is puppies usually outgrow excitment peeing, just be careful you don't create submissive urination.
Dogs and Submissive/Excitement Urination - Fixing Submissive/Excitement Urination in Dogs