She’s Charlotte Meredith Grote (assuming Mildred didn’t make that up; you know what she’s like). But she frequently refers to herself as “Carlotta”, I assume to make herself seem more exotic.

Similarly, Miss Haversham’s name is not actually “Mildew”, and the guy who hangs around is named “Glenn Durgan”, not “Glyn Durban”, or “Goblin”, “Gremlin”, “Gürm”, “Glem”, or “Gimli, son of Glóin”.