my mom thought all photos had to be taken with us kids squinting into the blinding sun (her with the sun in her back) in order to get enough light for the camera
Depending on the camera and film she had, she might not have been totally wrong. Or, at minimum, this likely allowed a higher "keep" rate for shots without futzing about with the ISO setting, exposure compensation, or anything else (which might not have been available if she was using a basic P&S).
i don't know how old you/your moms are, but chances are that even if you're younger your moms' mom probably did that because she was taking pictures with something like kodachrome 64 than unless you're in the sun it ended up having 0 shadow detail. so it was better to have a least a squinting picture of a kid than have half their face be complete darkness.