A belt-it-out song would be good, because Lucy belts and screams all her songs (most of it isn't supposed to sound pleasant). You should probably go for a song that shows a little campyness, that you can really play up because everything Lucy does, after all, is over the top.
Maybe something from Seussical? Just a suggestion.
I was in YAGMCB last year, and even though I wasn't Lucy, I still know the show, so I thought I'd help.
"Love is a many splendid thing, love lifts us up where we belong, all you need is love!"