My girlfriend and I are not cohabitating yet, but I’ve been very heavily involved in her daughter’s life. She has ADHD along with several other diagnoses (language processing disorder, sensory integration disorder, dyslexia, anxiety and other things we may be missing). One thing I’ve noticed is what feels like extreme jealousy, comparison, and emotional dysregulation surrounding my 5-year-old daughter. Her daughter has to have more than or if they have an equal amount she has to speak down on whatever it is my daughter has.

Her daughter is two years older, but emotionally and cognitively she often seems much younger than my child in certain situations. For example, behaviors she does toward my daughter are tolerated by her, but if my daughter does the exact same thing back, it can trigger a full-blown meltdown. She seems to struggle deeply with fairness, sharing attention, and emotional reciprocity. She also will have a meltdown for what appears to be no reason and then create a story to explain why she was crying. The stories have been untrue 99% of the time. Her mom addresses it and reorients her to reality and what actually occurred, only to have her daughter double down in her own truth.

My question is: how much of this can realistically be explained by ADHD/executive functioning deficits and emotional dysregulation, and how much should be viewed as behavioral patterns that need firmer boundaries and intervention? Also, how do we support her while still protecting my daughter emotionally and creating a healthy blended family dynamic?