I feel your pain. I have a female YB granite the same age and while she was a good eater at first, once she hit about 500-600 grams she put herself on a small rat every 5-6 week feeding schedule. She hasn't broken 1000 grams yet either.
She's healthy with good body condition, just not a big eater. I figure on throwing my pastel YB to her in the fall of 2018 if she gets over 1300 grams.