Bringing in a second dog was a game-changer for my spooky girl. She has become so much more well-adjusted and confident, and I love to see how well they interact with each other. There were three years in between my adoptions, and in a way, I wish I had done it much sooner (though then I wouldn't have ended up with my silly Nova Noodle).
I have two females. My spooky girl is also alpha. I had assumed that she would get along best with a goofy boy. After fostering a couple of wonderfully sweet boys, she wasn't really clicking with them, and I started to wonder if she actually preferred being an only dog. As a last effort, I brought home a sweet little female foster-with-intent, and they were instant companions. Basically, I let my first girl choose my second, and the rest is history.
Best of luck to you as you think about adopting your second!