What if a mother is resentfull of the caregiver daughter, while very sweet with the one who never offered anything?

You know they say a child will justify the abuse of the parent. They try to be a good child hoping the parent will love them. I think it's sort of like that with a parent who seems to favor the child that really Doesn't show the parent a lot of attention. The parent goes out of their way for them hoping they will show some attention to them. This favored children tend to be self centered.

RosiePap I feel your pain.
My mother has a seizure(?) and my visiting brother LEAVES THE ROOM! He is still in denial that there is anything wrong. Her hallucinations are just her waking from a dream and being confused, etc.
He travels the world for his job, he has no children and unlimited spending money.
I will say that he spoils my son to no end, so that’s something.
Maybe your parents were/are trying to buy her love. It’s obvious that you love her, but if your has never made time for her...
Maybe your Mom’s brain is ‘stuck’ in a specific time when your sister needed help in her life. That’s all she remembers.
This whole brain thing is so tough to deal with. Know that at the end of the day, you are doing the tough job. The hardest job of all. And you do it because you love your Mom.

Indeed, JoAnn29 and Basdavis, you are both right. My sister is very manipulative and always says to my mother to do what she likes. After at least 10 yrs of really hard work taking care of my father and after he died, continuing with my mother, I feel totally excausted. My sister not only never helped but she was harsh on me. She doesnt think much of me, to be honest I think she hates me. See, during the time Ive been taking care of our parents, she went abroad, she had children and she always had an excuse to disappear, while I was always here for them. I dont have children, but I do have a family and a job, too. But who cares? My mother as my late father too, all these yrs didnt want to bother her with their problems, but they did want me to solve all their problems. They gave her more property than me, even I almost begged to get it, for I never had the time to make money because I was always busy taking good care of them.

Indeed, JoAnn29 and Basdavis, you are both right. My sister is very manipulative and always says to my mother to do what she likes. After at least 10 yrs of really hard work taking care of my father and after he died, continuing with my mother, I feel totally excausted. My sister not only never helped but she was harsh on me. She doesnt think much of me, to be honest I think she hates me. See, during the time Ive been taking care of our parents, she went abroad, she had children and she always had an excuse to disappear, while I was always here for them. I dont have children, but I do have a family and a job, too. But who cares? My mother as my late father too, all these yrs didnt want to bother her with their problems, but they did want me to solve all their problems. They gave her more property than me, even I almost begged to get it, for I never had the time to make money because I was always busy taking good care of them.

I think it also has to do with the fact that as the caregiver, we have to be the one that sometimes says ‘No’ or makes them do things they may not want to do.
I have witnessed that they are often meanest to the ones that are closest to them. It is common, but doesn’t hurt any less if you are on the receiving end of the venom.
In my case, I am my mother’s caregiver. She is only mean to me when no one else is around. My husband and son don’t see it, for which I am actually grateful in the cas did my son. I don’t want him to remember her that way.
My brother, who lives out of state, swoops in for a fun weekend. She praises him, he can do no wrong, etc.
I have to look at it as parenting. We don’t always get to be fun, but it means that we care.

Yes, very common. Some parents tend to favor one over the others and usually that one that takes advantage and never do anything. I have my ideas why this happens. The favored one is never asked to do anything. Usually has a manipulative personality so knows how to work the parent. Then there is a child that has some compassion and feels some responsibility to the parent. You have become the parent and the parent the child. Like a child, parent Doesn't like to be told what to do by caregiver or Drs. So in comes the favored child that puts no restrictions on Mom. These favored children will be the first in line for any inheritance. With my sister, it was an attitude thing that she got away with not doing.

Rosie,
Can you elaborate a bit more? BTW, this is not uncommon at all!