Jane prior to the incident that caused her change was a very caring soul, always ready to help those in need. This is shown when she displayed concern for Jeff after his fight with the neighborhood bullies. She was never late for anything, especially school.

This caring demeanor would fade after Jeff killed her family and burned down his house with her inside of it. Jane soon made it her goal to exact revenge on Jeff for what he had done to her. She became cold and heartless, dead set on killing Jeff. This obsession made her mentally disturbed, causing her to have flashbacks about the night she was burned. The obsession also caused a severe case of psychosis, making her believe that by killing the victims Jeff was stalking first, his rampage would stop.

Jane is a sexual being and isn't ashamed of her orientation or number of partners. Jane herself has stated that she was primarily straight but has shown some bisexual tendencies. It could be speculated that her carnal interludes are a way to cope with the trauma from her childhood as she made a comment saying that the "'Big O' makes the screaming stop". Jane would use her body and feminine charms to manipulate people to assist her to kill Jeff. However, though ironic on many levels, Jane considers herself hideous despite coming out much better than Jeff and found attractive by many.

Jane has been shown to harbor some sociopathic traits. It is very difficult for Jane to sustain a friendship or, at the least, a partnership. This, of course, has the exception of Sally and Slender Man. Jane is prone to betraying and/or abandoning her partners if the situation does not suit her but this has lessened to a degree after being sanctioned by C.A.P.S.

Jane's relationship with Jeff is complicated at best. While there is the constant her desire to kill him, the two have seemed to develop an extreme variant of a love/hate relationship. On most occasions, Jane loathes Jeff in her presence and her urges to kill him are unsatiable. But sometimes, either to her carnal desires or Jeff's manipulative nature, Jane's entire outlook on Jeff can flip dramatically. Their shared past and sociopathic natures seem to both draw them together as well as drive them to kill each other. There have been several occasions where the two have teamed up and even slept together only to turn on each other moments later.

((Source: http://creepypastafiles.wikia.com/wiki/Jane_the_Killer))