You seem as a very good daughter. This is the first I wanted to say.
I’m not or will be a mother so I can’t even talk from experience about how much love you can have for your kids. Equal, different, conditioned...
All I know is that people establish different kinds of connections among them based on many factors as laces of blood, characters, the way each person evolves...
There’s few you can do to change it apart from following your own path, stand up for yourself and do what you consider more fair. No matter how they behave. If you think you are doing something right and accord to your principles, do it without expecting.
Many times you can’t expect what they cannot offer.

I wrote in the post above if you ever tried what Mickey Cheeky suggests. I mean to talk directly with her and tell her how you feel?