I've always thought putting her fleeces/ blankets on a hot wash, every fortnight, was enough (unless "bodily fluids" from either end are involved, in which case it's put through the machine immediately).
She also sleeps on the bed: my duvet cover etc. is changed every weekend.
However, a friend looked slightly horrified on hearing this: apparently I'm even risking my cat's health by not doing hers at least weekly too, preferably twice. 
I now feel terrible: obviously my cat's wellbeing is a priority. So please be honest if I need to improve my ways... 