In addition to the other comments,
You are probably 'bitter" because your Mom is not like how you think she should be.
She is not your "ideal" Mom nor what you think, a "Mom" should be. Thus you resent her. And sure, she ain't a lovely person... but, well, that's the Mom you got.
And you are the Daughter she got.
Your Mom, is NOT a "Hallmark" greeting card type Mom. You resent that.
But she will NEVER EVER be, that kind of Mom.
And sure, she has caused issues with your Husband and in-laws too.... and no one cares for her... YOU included.
Thus, you 'resent' her.
She is simply... NOT the kind of Mom you think she should be or that you have idealized in your head, about what a Mom "is."
Thus you resent her.
One of my siblings, hated/resented my Mom too. Because, to her, our Mom was NOT the type of 'parent' she thought our Mom 'should' be. So all her life, she pretty much 'hated' and resented our Mom. The problem.. was her... NOT our Mom. The problem was that she just NEVER 'accepted" our Mom for who she was... nor, was she able to separate... fantasy from REALITY.
In her head, she thought our Mom should be and had to be, just like the "fantasy Mom" she had idealized in her head.
Well... too bad, that is not reality. That is a problem of the person themselves and not being able... to, just accept and cope, with what you have for a parent.
Not having a sense of entitlement.
all the best,
Susan