number one tell her to switch to a non-clay litter. even ones that say dust free have a lot of dust. it can make healthy cats sick and if the cat already has asthma i hate to think what it could do.
alternatives are the crystals (never tried them, they're expensive), swheat scoop (made from wheat, better but still has some dust because it's so fine. nontoxic though) and the ones made from recycled newspaper (this is what i always recommend, it's cheap and no dust)
if she uses a litter box with a lid, get her to take the lid off. ammonia can build up in a litter box and cause respiratory problems. better without a lid so the poor kitty can breath while 'going'.
also if the house is generally dusty an air purifier or some filters can work wonders. if she has a furnace or forced air heat or whatever and there are cold air registers, you can buy this blue filter sheeting that's like $3 a roll, cut pieces to fit and stick them on the inside of the registers. keeps a lot of dust from coming through and it's cheap. just have to replace it every few months. this will cut down on dusting around the house too, which is a plus.
they could also set up a humidifier if they have one, and try to avoid anything smoky or perfumy in the house, don't use harsh cleaners around the cat etc.
I'm singin' here to get rid of fear
Hope it disappears right here with the rain
But I know life is pain, not like a fairytale
Meaningless to pray, so just goin' on my way