I feel like her being this SJW-ish character was a bit ass thing of her to do. I mean I know she's only worried about Mashuu but still. Appearances are deceptive.
Like in case of his dad, she thought he was a terrible, neglectful dad, who probably lives an unkempt lifestyle, doesn't take care of Mashuu for some reason, and named his second son with the suffix "-ichi" (one) in his name --when he just turns out to be a struggling single parent.
She is doing it again.
And this time, she sees herself as his self-appointed hero, it seems. "I have to save him." Two years ago, she was conflicted about whether she was meddling in his life too much, and now she's head-on aiming to save him from whatever she thinks is happening in the house. Is this character development positive or negative (as in, actually intrusive)?
After taking his mother's photo in consideration, Mashuu might just be adopted-- with his brother actually being the father's first son and the '-ichi' suffix justified.