I don't really know much about music, like in that technical way (I have no idea what mezzo soprano is) but Matilda the Musical just closed and it has some nice songs. My favorite is Naughty, but it's just a suggestion. Hope it's helpful :)

Awesome! I'm in Shrek too. I don't have any songs in mind at the moment for suggestions, but if I were you I would choose something you already know and love; don't learn something new. Choose something that is a similar style to the songs in Shrek, and something that displays your range. Good luck and let me know how you go!