Congratulations, you have captured a lot of her vivacious personality in your very first portrait...a tough thing to do. And you have courageously chosen a medium (watercolor) that is difficult for many portrait artists to handle.
Could you post your original photo and your charcoal drawing?
Sometimes when we begin our work with a poor photo resource, it is nearly impossible to overcome this handicap.
Could you take another photograph? If you do, use a single source of light and have your girlfriend pose with a closed-mouth smile. A really good photo would be so much easier for you to work from and it would increase your chance of making a successful painting.
Ciao