I'm a good singer but...?

I have a very good tune and im best at soprano but my voice isnt strong enough and sometimes my voice get croakey and rough and i need tht to end like especially in musicals its ok because im a good actress which means tht i cud cover it up with acting and sweeney todd is being considered at my drama company and im most likely going to b mrs.lovett IF WE DO IT (thts the parts we discussed so far haahaa) but yeah its my dream to play tht part and even in the movie the actors couldnt sing so thts the good thing about tht play but yeah i know the part like the back of my head even tho i have a decent voice already, i want a better one I MIGHT BE GETTING A COACH SO DNT EVEN BRING THT UP also olive oil is supposed to help...? just some exercises i need please help :/