That sounds like puppy behavior. Interesting that she's doing it now, unless somebody has been encouraging her. From the sounds of it, she's trying something new to demand attention. For now, I would treat it the same as puppy biting. In other words, when she does it, you scream like a puppy -- high pitched "ow!!!!" -- and then you turn away and ignore her. (A lot of times the noise itself will stop a dog in its tracks.) Walk away and leave the room if need be. When you come back, tell her to sit or do something else polite before you give her attention. If she doesn't get the "reward" she's seeking for her mouthing behavior, it should eventually extinct itself.
It also sounds like you might need to do a bit more for her exercise needs if she's that keyed up and needy. Just letting her out in a fenced yard is not going to get 'er done. She needs good, focused cardio to shake off that mad energy. Springpole, flirtpole, treadmill, fetch, tug, running next to a bike or a jogger, etc. Doing the polite greeting and then going into the exercise is a good way to reward her for good behavior.
*Disclaimer* Giving training advice over the internet is kind of a crapshoot. If you're still having problems, make sure you consult a trainer/behaviorist.
Lindsay & the Gravity Dogs
"Though she be but little, she is fierce." -- Shakespeare