@Liquidxlax Some women just have the chassis for headlamps that big; I've personally had experience with a woman who's breasts were easily larger than my own head (and I have a big ass head) and she thought her boobs were brilliant, no issues with them at all. For every woman with back pain there is one as big or bigger that doesn't. It's a bit like how some dudes get sore shoulders wearing a moderately heavy backpack to college while there are others who do 20k full kit marches in the military like they are out for a Sunday stroll.
Being a mum certainly helps though. Chances are having to carry you and your sister about on a daily basic strengthened her back quite significantly