Let’s not forget, Regina did go 28 long years without using magic, and during that time she still was manipulative and mean, and to some, truly evil. For her to put down the magic and try to become a better person will take more than just not using magic. She needs a complete personality make-over. How does one atone for the murder of their own father (Henry Sr.), lover – Sheriff Graham, and possible countless others?
She may not have had magic but she had power which can be just as addicting. As Mr.Gold said magic is power so in a way this is the first time in a long time she’s giving up both sides of her addiction.