My conclusions on the Carlotta subject lead me to only one thing: Carlotta was based in many people.
According to phantomoftheopera.ro, someone from that site went to the opera library and read that:
"Mademoiselle Krauss (a diva): became ill. She couldn't sing for 10 days. Don Juan was replaced by Faust." (April, 1879)
Christine Nilsson, the woman which Leroux based Christine Daae's life and singing career on to make the story more interesting, had a great rival. Another soprano, Adelina Patti. Although no evidence of them arguing or even having ever talked to each other is known, Adelina's personality was pretty simillar to Carlotta's in the book. Also, CAN WE IGNORE THE FACT THAT ADELINA'S SISTER'S NAME WAS CARLOTTA PATTI? (Excuse the caps). Wikipedia says that Adelina was a coloratura diva, and even her face looks like the one of a diva's. She is spanish, just like the book Carlotta. She sang Faust (By Gounod). And we have recordings of her voice thanks to the Paris opera house (Which can be heard on youtube). Also, another funny thing is that, much like the Andrew Lloyd Webber musical Carlotta, she was married to a tenor who sang with her, Ernesto Nicolini (Much like Piangi).
Carlotta Patti was weel-chair bound though.
Another inspiration for the character, was the short-tempered diva Marie Miolan-Carvalho, who also sang Marguerite, but only when she was really old, but it was a big fop, according to many sources I have.
And the last inspiration, was Rosa Carron, the singer who was singing when the counterweight of the chandelier fell. She was in the middle of an aria, when the counterweight fell on a woman.
Carlotta was inspired by many people.