I agree 100%. I understand the desire to "explain" her actions with these labels but there has been nothing to suggest that Angela is mentally ill, drug addicted (only marijuana use has been confirmed) or even intellectually challenged. I'm not going to try to excuse or justify her behavior when it is quite possible that she is just a horrible parent and human being. She is no different than countless other young, self absorbed mothers except she took putting herself first to a tragic extreme.
I agree that while we would like to "explain" her abhorrent behavior, it may just be she is a horrible, self-centered person.
I do not agree that age is a factor. While she is "young" compared to my age now, compare her to most 26 yr olds you know.
My two oldest are over that age, but at that age they both were responsible adults with careers.
At her age I had two children, aged eight and six, was living in our second home, and was in the process of adopting our third child who was the son of my drug/alcohol addicted sibling. My husband and I were respectable, productive, caring parts of society.
At her age, Angela made choices that led her to the life she was living and the people she surrounded her children with. It is a shame, but she was old enough to understand the decisions she made, and she chose to put her children at risk for her own selfish desires.
ETA: I grew up in a VERY dysfunctional home with abuse and a violent in-and-out alcoholic step-father. So while childhood can affect choices, we can ALWAYS choose to go against what we grew up with.
IMO.