"like a free falling elevator" shows that Melanie has stage fright. which often gives you the feeling that your stomach is falling.
"She crept slowly over to the podium and bent the microphone toward her mouth, like the straw in her pink lemonade." she moved the microphone to her mouth like a straw.
Rewrote in another words
"Being similar to a plummeting elevator" indicates that Melanie experiences stage fright, which frequently produces a sensation of the stomach dropping.
"Silently and cautiously, she approached the podium and tilted the microphone closer to her mouth, resembling the way a straw reaches for a sip from her pink lemonade." She adjusted the microphone position, mirroring the action of a straw reaching for a drink from her pink lemonade.