Is it possible for a Muslim woman who does everything right in accordance to her deen except the fact she does not wear hijab to enter Jannah?

Yes it’s possible as long as she is not openly rejecting Allah’s laws. Sometimes a person knows it’s a sin but she is trying and she asks Allah to help her. She is eligible to go to Jannah. But if a person is arrogant and rejects Allah’s commands, then that is a form of disbelief.