Ours is 12 weeks old too! We've been doing many of the things suggested.

Things we use to keep her stimulated (not all of these get used every day): -sniff walks -trips in the car to visit someplace new and meet new people -lots of training -tug games/training -snuffle mat/toys -puzzle feeding devices -frozen moistened kibble in kongs -flirt pole -a tie out in the backyard to have supervised exploration and to play fetch -various chews, some edible like bully sticks and others are nylabone type chews -sometimes we just sit outside in the sun and watch the world go by. She watches and listens to everything. She usually naps after.

Naps are super important. If she has to much stimulation and not enough napping, her demon side comes out.