BETA adult. Or any quality dried food (I'm not going to be drawn into the raw food debate)
However, it look like you think she is underweight (which I'm guessing at from your "only just keeps a healthy weight" comment) and want a diet to get her to be the "proper" weight.
If she is behaving normally, looks healthy, no diarrhoea and runs around like a demented GSP can - ie a normal puppy, then I wouldn't worry about her weight. She's so energetic, she'll burn off any food you give her. SHe's better being a skinny athlete than a lardy slouch!
This is a really common question that vets get asked by owners of new dogs. Skinny is normal