
At 8 weeks I wouldn't expect a daily weight gain, she hasn't lost any weight. The vet must have thought she was the right weight for her build and he/she has had their hands on her to feel if she is too thin/dehydrated.
Have you tried her with tasty things mixed in with her kibble, grated cheese, cottage cheese, pilchards, she may be a faddy feeder and when they are so small you can't afford to leave them till they feel hungry.
Have you tried stuffing a kong, putting her kibble in a treat ball to make things more interesting/challenging?
Look for recipes for "satin balls", high calorie so she doesn't need to eat much in quantity.
http://www.lowchensaustralia.com/health/diet4.htmHope she bucks her ideas up soon as she has been a worry for you from the start.