Hey....you cannot compare her to any other lab or breed regardless of age etc..........as ur dog/ pup is unique. Did you know dogs like yours are called designer dogs and are very popular with celebs in Hollywood. The designer dog that you have I have not heard of it ever so u r very lucky to have her.
As for health feed her a good commercial diet or home made diet and she will be fine. To see if she is underweight or over weight, try and feel her rips, if you can feel and count them then in general she is in good weight, but this does not mean that you can see her rips when you look at her. Only when you feel her side you should be able to feel her rips.
She is still very young and it is better that she is lean till she is atleast 12 months old as you really dont now what she will turn out to be and you should not but undue weight on her bones and body structure. Give her calcium and vitamins as per the vets advise.
All the best !!