The title says it all, but I'm curious because it isn't obvious how a theorem prover came to be named 'Isabelle'. Was it named for a person? I couldn't find out by some Google searches.
A little google-fu (and my own memory) tells me it was apparently named by Larry Paulson after Gerard Huet's daughter.
Gerard Huet happens to be one of the people behind the less poetically named Coq theorem prover.