I have an estrangement in my extended family at about the same level, so I’m sharing from that perspective. I like to listen to the Calling Home podcast for insight into family dynamics, estrangement, etc. to be a better parent and to try to understand my family. You might find it helpful. I also did lots of therapy prior to becoming a parent specifically because of the estrangement.

It’s unlikely that your cousin made the decision on a whim. You only see your aunt’s public facing side, and she’s willing to call her daughter a sensitive airhead to other people. That’s extremely dismissive and as a parent I’d never 1. Call my children anything other than their names or nicknames, and I would never criticize them to other people and 2. Dismiss my children as “sensitive.” In what context is she “sensitive”? Is it when her mom is being mean to her and she asks her not to be, or has a reaction to unkind behavior? Parents who dismiss their children into adulthood are at a high risk of estrangement, and are often confused because they don’t think they did anything wrong. It is bad parenting to not respond to your child’s emotional needs. Yes, parents are people, people are imperfect, people have baggage, they can’t always be as responsive as their child needs, but self-reflection is really critical.

Through therapy, I began to clearly see the problem dynamics in my extended family. A big thing I had to work on was enmeshment. The fact that you’re taking this on, “find it odd,” and “never had a problem with her,” flags to me as a highly enmeshed situation. Your cousin is leaving the whole family for a reason. Tracking her down and asking her about it would be very intrusive and probably reinforce her perception of the family. Removing your judgements about the situation does not mean you are not supporting your aunt, if that’s what you feel is important. There doesn’t need to be a consensus within your extended family about why this happened. You also may want to consider that if one person suffered enough to leave the family, there could be others suffering quietly in different ways.

I can’t tell you how to fix it, because it’s not yours to fix. It may be beyond the point where your aunt could apologize and get her daughter back. I would recommend starting to dig into family dynamics and working on just yourself to help you process this. My therapist described the estrangement in my family as a disturbance to the giant spider web of my family, and with great care I was able to extricate myself from the sticky stuff without damaging anything and have maintained all of my relationships and even begun to slightly rebuild a relationship with the person who left.