How to get a good accent for Mrs. Lovett from Sweeney Todd?

I'm in an all boys school, and we are doing Sweeney Todd in January.
I'm trying out for the part of Mrs. Lovett and I was wondering how to
sing her songs, put on her accent and how to act,as a boy, to get the
part???
How to sing her Songs......??
How to Act for Her......??
How to Put on Her Accent....??