Does oyster shell help with a good diet in budgies and finches or do harm?

well i had a problem with my female budgie egg bounded..my vet told me she probly was to young and or else didnt have the proper diet..so after the egg binding i was told that oyster shell is very good in calcium and healthy for my birds...they have everything they need like mineral block cuttle bone you name it and always make sure of fresh water everyday...i really would like to know cause they will not touch any greens i try giving them..oug plz help...should i buy a uv bulb to supplement the lack of sun they dont really get ...thanks for reading and plz help