How much has the breeder told you to feed her per day?
Normally 8 week old pups if only being fed kibble, should be fed around 2.5 cups per day, so you divide this total amount over 3 meals. For your pup being as small as she is, I would probably start her off on approx 2 cups per day rounding to say 3/4 of a cup per meal for 3 meals a day. I would see how she goes with this amount over the next couple of weeks and if she is gobbling up each meal in typical Labrador gutsy fashion, then I would increase to 3 cups per day, i.e. 1 cup per meal, by the time she is 10/11 weeks old.
The following will give you an idea on what the recommended number or cups per day is for Lab pups of average size at the various ages. You need to take into consideration your girl's size and the fact that she is lighter than the normal Lab female puppy weight, so you will need to adjust the following, hence my recommendation to start at 2 cups per day and increase to 3 cups per day by the time she is 10/11 weeks old if she can handle that amount then. You will proably find that 3 cups is all you need to feed her even as she grows as you need to be monitoring her growth and weight and adjust their food accordingly and you can do this by weighing her weekly at your Vet. Whilst we are on the subject of Vets, do you have a Vet and are you going to get your Vet to give her a checkover?
8 weeks - 2.5 cups
9 weeks - 3.0 cups
10weeks - 3.5 cups
11 weeks and older 4.0 cups
Remember the above advice on how much to feed her is based on feeding her kibble only. If you decide to add in things like mince or chicken wings or chicken necks etc, then you need to reduce the kibble accordingly. You may need to tweak the qtys of food you give if she is not putting on enough weight or putting on too much weight.
When I got my boy as a pup he was also being fed Advance by the breeder and he gave me a bag to bring home for him, but he wasn't just being fed kibble, he was getting mince, veges, yoghurt, sardines and raw eggs added to his kibble, so of course the kibble component was reduced due to the additional things he was being fed. I found that whilst he was on Advance, his poos were too soft and another few Lab puppy owners that I knew also had the same problem, so a few of us changed over to Nutro and poos were normal within a few days and his coat also was a lot glossier. My older Lab boys were also on Nutro, the adult version which they had been on for a few years before Nutro was banned from being imported, but when they began manufacturing Nutro here in Australia, I put them back on it as they all did very on it and so did my pup. However, last year, I changed them over to a locally manufactured kibble, Black Hawk Holistic which they are all doing great on.
I would suggest you continue feeding your girl Advance as that is what your pup is used to and if you want to change her over to a different brand, do it at a later stage or sooner if she has any issues on it, and either way if you do actually swap her kibble, then make sure you swap her over slowly to the new brand by mixing in some of the new food in with the Advance and slowly decreasing the amount of Advance and increasing the new food over a two week period.
Also in line with what some of the other posters have said, don't follow the feeding instructions on the kibble manufacturer's bags as they always recommend way too much. Obviously this is in their best interest, as you have to buy more but meanwhile the poor dogs are getting fat.
My lab youngster was playing with a Lab youngster around 16months old at the dogpark yesterday and I was chatting to his owner who told me she feeds her boy 5.5 cups of kibble a day, in one meal She is a new Lab owner and I told her that was far too much and told her that her boy should only be having around 3 cups per day as he is carrying too much weight (told her in a nice polite way) . I advised her to start reducing the amount she is feeding him straight away but to reduce it slowly so that both he (Lab) and she (owner) doesn't think he (Lab) is starving, but to aim to have him down to 3 cups within a month and to give him two meals per day by splitting the total qty over two meals, rather than as one lump meal. I also told her she can fill him up with grated carrot/mashed pumpkin if she wanted to reduce his intake quicker. I ran into her and her boy at the dogpark again today and she quite proudly told me she has reduced his meal last night down to 5 cups from 5.5 and will begin giving him two meals from tomorrow and continue to reduce the number of cups over the coming weeks to get him down to 3 cups. I told her well done and her boy will reap the benefits with weightloss which will in turn reduce the chances of any joint issues.
If you need any more diet help with your pup, let me know and feel free to PM me.