If it is auto then not much you can do about a rough veg she will produce what she produces. If shes a photo then the rough start to veg should be just fine as long as you let her recover before you put her in flower.
As far as what you can give her to fatten up the buds would be any type of nutrient for the bloom cycle. Also if you can get your hands on a bottle of Advanced Nutrients overdrive (a nute that you use the last 2 to 3 weeks of flower) i swear by this product. Within 24 to 48 hrs after starting overdrive i can notice a difference.
I strictly use advanced nutrients line so i use sensi bloom parts a & b, big bud, bud candy, rhino skin. Then week 4 stop big bud and start overdrive until the end of week 7 then i use flawless finish. Those are the nutrients i use in flower. As long as you are using a bloom enhancer for fruits and veggies or flowers you should be ok. Try to stay away from anything high in nitrogen during flower too.
Im not sure what lines of nutes you will have access to in your location