The lyrics "Why would a fellow want a girl like her?" come from the song "Stepsisters' Lament" from the musical Cinderella by Rodgers and Hammerstein. The song is sung by the stepsisters who are expressing jealousy and confusion over why the prince would want to be with a delicate, lovely girl like Cinderella instead of a more solid, usual girl like themselves. They describe the girl as "a frail and fluffy beauty," "a frothy little bubble with a flimsy kind of charm," and contrast her delicate qualities with their own sturdiness. They question why the prince is "going crazy" over such a lovely girl and why he can't prefer someone "merely me," meaning a more ordinary girl like themselves. The song is essentially about envy and the stepsisters' inability to understand the prince's attraction to Cinderella's unusual charm and beauty.
If more details or full lyrics are desired, those can be provided as well.
