I have a GSD who is a year and 8 months old, she only weighs 62 pounds, I heard that they continue growing till the age of 3 yrs old is that true?

I have a GSD who is a year and 8 months old, she only weighs 62 pounds, I heard that they continue growing till the age of 3 yrs old is that true?

Also about her weight the vet says she is perfect all blood work normal and he says her weight is just fine but I was always told you should be able to feel the ribs and only be able to see them when they inhale. We had her on Royal Canin for German shepherds but after not seeing a change in her weight in a year I tried the chicken soup for dog lovers, that didn't go over well she didn't like it so after a 2 months we now have her on Eukanuba naturally wild New Zealand venison and potato formula, she gets an egg and fish oil capsules in it and she loves it. The bag says to feed her 3 cups per day but I have been feeding her 5 1/2 cups a day cause she is always hungry and to me she just looks like she's poor pathetic starving dog. There has been no change in her weight, what else can I do, will she hit another growth spurt and fill out or is this just her size? Also tried the raw food but a grocery stores charge an arm and a leg for everything, her food costs $50-$70 a month on the raw food it was like double.

One more question I promise, how much fish oil capsules should she get per day and does it help with shedding? The shedding is getting outta control I'm vacuuming twice a day and using the ferminator deshedding brush twice a day on her.

Thank you,
Diane