Practicing multiple languages

I've noticed that my mom always chooses keys so low when humming songs, that she can't reach the lowest part of the song, in spite of the fact that her vocal cords definitely have the ability to reach high notes without hurting themselves. I got this information from her abusive insults day by day towards me and other family members. She would yell loud and sharp for quite some time and never go for water immediately afterwards. She never caught on any disease for that as far as I can remember, and her voice quality hasn't changed. I'm quite the opposite. I can't resist using my vocal cords wrongfully when having quarrels with her. So when the thing is down, I will need water and some rest to recover. But I would be ok if I was using them right singing songs loud and high. So earlier this day when I caught her humming in an overly low key again, my curiosity took me. I made her try a normal key for female and of course she did it well with the “high” notes.

She then told me she is afraid of notes too high coming up with the song going on. With my knowledge, the exact song she was humming doesn't have such high notes. So she is hindered by her lack of musical knowledge to make some progress with singing.

And I thought there must be a reason why she would be so afraid of cracking, I asked if there was someone laughed at her but my question was ignored like most of my questions. Or maybe she treated that question as a provacation which led her to try the normal key. But the reason of her fear must be hard to dig out so I quit.