AITAH for being angry at my mother for allowing my sister to meet my son?

A woman has spent years dealing with severe verbal abuse and physical violence from her sister, including a shocking assault where the sister repeatedly punched her in the head and ended up breaking her own fingers. After multiple cruel incidents—especially during tough times like her divorce and health scares—she finally cut off all contact to protect her mental health. The sister has since been diagnosed with untreated ADHD and BPD, but has shown no effort to change or seek help.

This year brought even more challenges: a brutal pregnancy full of complications, followed by the birth of a son who needed emergency heart surgery as a newborn. With another operation ahead, the new mom set a strict boundary—no introduction to her abusive sister, ever. Her mother reluctantly agreed at first. But during a relaxed Boxing Day visit, while the exhausted parents napped with grandma babysitting, the sister suddenly appeared, held the baby, and snapped photos, leaving the mom feeling completely betrayed and worried for her child’s safety.

‘AITAH for being angry at my mother for allowing my sister to meet my son?’

The strained relationship between the two sisters had been building for years, filled with constant belittling and aggression:

Two major incidents in 2023 pushed things to the breaking point:

The aftermath took a serious toll, leading to no contact:

The betrayal happened over the holidays:

Things escalated further with health and privacy concerns:

This story hits on some heavy family dynamics: long-term sibling abuse, parental enabling, and the fierce protectiveness that kicks in once you become a parent yourself. The sister’s history of violence—culminating in an assault bad enough to break her own hand—isn’t something to brush off, diagnosis or not. Untreated BPD and ADHD can fuel impulsive, harmful behavior, but they’re explanations, not excuses.

Many see the mom’s actions as a classic enabler move: avoiding conflict with the aggressive child by sacrificing the other’s boundaries. Family therapist Lori Gottlieb often talks about how parents sometimes “peacekeep” at the expense of one kid to avoid blowups from the other, which only prolongs the toxicity.

The real issue now is child safety and trust. With a medically fragile baby, any breach—like strong perfume, unwashed hands, or unsolicited photos—feels like a direct risk. Going low or no contact isn’t “cutting off” family; it’s prioritizing a vulnerable child’s well-being over forced reconciliation.

Better approaches include clear consequences: no unsupervised time with grandma, and skipping events where the sister might appear. Therapy for the poster could help process the guilt, while firmly holding the line protects the next generation from repeating the cycle.

Here’s the comments of Reddit users:

The overwhelming consensus online is clear: the mom crossed a major line, and protecting the baby comes first—no one’s calling this melodramatic.

Most people urge immediate distance from both mom and sister:

Many suspect the visit was deliberately orchestrated:

Others highlight the enabling pattern and call for strong boundaries:

Stories like this show how old family wounds can reopen the moment a new generation arrives—parents often hope a baby will “fix” things, but boundaries aren’t optional when safety’s involved. The poster isn’t overreacting; she’s safeguarding her son from proven toxicity.

Have you ever had to enforce tough family boundaries to protect your kids? Would you go no contact here, or try one more conversation? Share your take below!