Could be alot of factors. But it.coudm be a mixture of breakage and the natural hair cycle.
It could be caused by stress as everyone is more stressed on the whole.
Changes in diets, hormones (as you said) and rapid weight loss.
Even though she mainly leaves it to naturally dry, does she tie it up damp or go to sleep with it damp as this can cause alot of breakage.
How does she tie it up, is it super tight with a bobble, maybe switch to a scrunchy or something similar which is kinder to the hair.
What pillow case does she have? Silk pillow cases are great for reducing breakage when sleeping. Does she tie it up loosely to sleep to reduce stress on the hair or does she leave it down and maybe suffer with alot of friction when asleep.
Is the shampoo she's uses still suitable for her needs?
How does she shampoo it? Is she rough? Does she roughly rub it dry with the towel or gently squeeze the excess water out? Does she also use conditioner? (Squeeze out excess water before conditoner is applied to the hair gets a stronger concentration of conditioner to seal the cuticle)
How does she brush/comb her hair. Is she rough with it and does she go roots to ends or start from the ends and gently detangles as she moves towards the roots.
What condition are her hair tools like? Is the hairdryer really old so the thermostat might not be working properly so excessively hot?
Does she look after her daughters hair with the same routine because if they have the same haircare routine etc then her daughters will be similar in condition? And it may be.mkre.down to the haircare routine than a bit hormonal change?
Sorry there's alot but these are the sort of things I would be asking clients if there was a change in their hair.