It’s very possible that this woman that shocked you has ADHD and her mother also has it. This kind of relationship can be explosive and loud and can be very disturbing and unsettling to others. Along with that it’s not unusual for the ADHD environment be what you described witnessing. The anger directed at you is also very common and the only thing you can do
Is what you did which was walk away
As quickly as possible.

This kind of person is not really capable of understanding how you are challenged right now with grieving over the loss of your mother.