I have a litter that is 3 weeks old today. One girl is smaller then the others. She is 2 lbs while the biggest boys are 4 lbs. Any tricks on getting her caught up. She is not as lively as the others but no slouch either. She is up and walking and seems healthy, just small. By the way the rest of the pups have their eyes wide open and hers are still slightly closed, she was the first born puppy.
Could she be a premie?
All suggestion appreciated.

Relax. As long as she is gaining, she is just fine.

Don't worry about her. She'll grow. The best example of this is my girl Lil. (click here)
I couldn't give her away (and I really did try) because she was so small. Later, I was very grateful that nobody wanted her.

Glad you kept her too, one pretty girl that doesn't look small to me. A great example Blue Knight.