She should pick the dressiest option on that website, and wear a simple shirt (i.e. nothing with fancy shmancy trim or necklines or distractions in general) and capri pants.
And not to hijack but man, if that blue print dress under Prefs is really an example of something someone would wear to a prom, everything old really IS new again.
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It is all 33girl's fault. ~DrPhil