A mother who's jealous of one daughter but not the other isn't unusual. In fact, I spoke with a woman recently who had just that situation. She had married an anesthesiologist and had traveled the world with him. They built a home together on several acres, and she was able to afford designer clothes and well-crafted furniture. Her sister, on the other hand, was married to a blue-collar man like her dad and lived modestly.
Their mother was extremely envious of the wealthy daughter and always referred to her as “the doctor's wife” in a haughty tone. She preferred spending time with her less affluent daughter because they had more in common. She rarely spent time with her other daughter, the doctor, and their two kids because she felt inferior to them. Even though the family did everything in their power to make her feel at ease, they couldn't stop her from running the same negative tapes in her head that said: “I'm less than. I'm lacking. I'm not as smart. I don't fit in here.”
When the couple divorced after 22 years of marriage, the mom wanted to renew the relationship with her daughter, but it was too late. The daughter had wanted her mom to be there during the good times and the bad...not just the bad. She accepted that some people had been jealous of her when she was married to a successful doctor. However, she could never accept her own mother's envy and, thus, no longer wanted anything to do with her.
Some people, like this mother, have flimsy egos that prevent them from having relationships with anyone who they believe is better off than they are. Being around a person who's smarter, more attractive, more accomplished, or more affluent is too hurtful to their fragile self-concept. This ugly part of human nature is why jealousy is aptly called the green-eyed monster.
People who are consumed with such envy aren't happy because they focus on what others have and what they lack. Being grateful is not a part of their daily spiritual practice like it should be. That's why “comparison is the thief of joy” is a powerful mantra that some individuals recite in their minds whenever feelings of jealousy creep into their consciousness.
Part of maturing is seeing our parents as human beings with frailties and limitations just like everyone else. Hopefully, you can stand back now, realize your mother struggles with jealousy and insecurity, and not take it personally. It has everything to do with her and nothing to do with you. Accepting her “as is” will bring you peace and relieve you of stress.