Yelling at complete stranger

This is out of curiosity, 10 years back my sister (8 years old at that time) while cycling around she complained about a woman yelling random things to her , she told whenever she sees her she yells. So I tracked this, watched this many times only when she sees my sister she tells otherwise she is okay, probably working lady. The thing is she is a complete stranger to us. It's weird at that time and very creepy I was only 12. Even she yelled when our parents were around.
Anybody have a clue what is going on her mind, it was not at all friendly/prank.
I saw her today which lead me here.

There could be a number of things wrong with this lady. She might be certifiably insane, or she might have anger issues. We will never know.

The best thing to do is to stay away from people who just randomly yell at strangers. Best keep to yourself and stay safe.