She also has the extended 'singing lesson scene' where the character does this with very little plot relevance at some length, and is more or less expected to showboat to the best of her ability. Some singers have been reported to stretch it out for at least 20 minutes. Others accompany themselves on the piano or other instrument, and for many years it was traditional to cut the aria Rossini wrote for the scene and interpolate some other piece that would show their voice off better.
Troubled Production: The 1816 premiere became legendary as a performance in which nearly everything that could go wrong went wrong - for instance the actor playing Basilio fell on his face and had to sing his aria while trying to staunch his bleeding nose with a handkerchief. There also were many boos and catcalls from an audience that contained many fans of Giovanni Paisiello, composer of an earlier operatic "Barber of Seville", who were affronted by Rossini choosing the same play to adapt and tried to disrupt the performance. Things got better starting with the second performance, though.
The 1944 Cartoon:
Non-Singing Voice: Singer Lee Sweetland subs in for Woody Woodpecker's standard voice actor, Ben Hardaway, for the Largo Al Factotum number, since Ben presumably couldn't sing that well, but Lee had his voice mechanically sped up so as to match Ben Hardaway's Woody voice.
for an example.