being Very theatrical myself I would always choose a musical theatre piece but this only works if you are willing to act it. If you want to do a musical theatre song and you really want to show off your voice go for something like memories from cats or hopelessly devoted to you from grease. Or you can really go all out to put on a show and do something like all that jazz from Chicago.
Or you can go the other way and do pop songs.with pop songs you can either go for something really upbeat like pack up by eliza doolittle (or any of her songs!) or you can do the slow meaningfull ones like make you feel my love by adele. I would always say do one which you are completely confident with and is entirely in your range so that if your voice isn't 100% on the day it won't be a complete disaster!
hope this helps! And GOOD LUCK!
OMG that's one of my little girl's favourite songs and Don't rain on my parade and I dreamed a dream.I was going to do defying gravity, but my voice is going. IT should be alright on the night but I want to have a back up, I was thinking no one but you from WWRY... xx