You are correct- she may never change. It may be not that she does not want to but at this stage in her life that she's not capable (lacks the introspection and spiritual/emotional/psychological/moral development)
You may be feeling guilt and grief because you are still holding onto the hope that things can be different (even if it is a subconscious hope) The guilt comes from the fact that you may feel bad about halting contact with her as her daughter. Both feelings are as a result of what you believe and tell yourself. You'd have to try to see the situation objectively; it is hard but not impossible.
Some internal dialog that you may resort to is "this is how she is; I accept that she has flows like anyone else, In order for me to move on, I've got to let go of the past, my expectations of her match her ability at this point in life, I know what is best for me/I tried and gave her a chance, I won't allow her or the past hold me down..."
You may use autogenic training to strengthen these affirmations or the ones you compose for yourself that you're comfortable with.
When You and Your Mother Can't Be Friends: Resolving the Most Complicated Relationship of Your Life by Victoria Secunda (Paperback - May 1, 1991)
Recovery of Your Inner Child: The Highly Acclaimed Method for Liberating Your Inner Self by Lucia Capacchione (Paperback)
She may not be capable because of having lived so long in her way, not having reached the spiritual development to move on (no epiphanies for her) Intellectual knowledge is different from emotional/spiritual growth.
It is hurtful as long as you allow it to hurt you. She is living as best as she could. This is in a way all she's capable of. It would be disappointing and hurtful to expect her to perform at another level that she had not yet reached.
Your affirmations and belief system can move you to the place where you want to be. It may take time and it would depend on you allowing yourself to get there.