DON'T EVER SCREW WITH THE TEMPO THAT'S WRITTEN! It is one of the worst mistakes you can make in an audition! Don't do it! ESPECIALLY with classics! The only exception to that rule is if you are going for something jazz-oriented and you are singing a jazzy version of something that is a classic, since classic musical theater and jazz often intersect.
For one, the casting director that's expecting the song to be the ballad it is will be totally thrown if you make it an uptempo...And they will focus so much on that and your performance may be missed. Then they will think you are inconsistent with tempos...
Do what you do best, within reason! LOL!
If you can improve "Show Me" by the time you audition, then that would be a better choice...if not, stick with "If I Loved You", but continue to work on "Show Me" because that's a more appropriate sound for Maria ultimately...They should be able to hear if you can get a different color from "If I Loved You", so don't worry about that too much...
Make sure that you have more than one song prepared that you're comfortable with, as that makes it easier for them and yourself when preparing to audition.