Little was known until Stephanie Meyer released The Twilight Sage - The complete Illustrate guide.
Jane, like her brother Alec, were considered the witch twins. Bad things happened to people who were bad to them, and good things happened to those who were good to them. This is why the scared village people decided to burn them at the stake.
When a human becomes a vampire, their personality remains unchanged. Thus enabling it to be stated that Jane was typically the same before being turned.