I felt the protagonist was justified in her belief that the mother loved her less than her brother. "No, not you, I don't want you! I want Jamie!" the mother says at one point. I think that is a clear indication of her preference for him.
Also I thought the protagonist's disability was physical, not an inability to feel connected. "I could not use my legs" she says at one point.
My take was that when she finally does something her brother couldn't she is free to stop competing with him and just appreciate him, even though it is too late.