Definitely all my posher friends, well most of them, live in such untidy homes! Even my own mothers house is a bit rank but then she’s getting old. She thinks hoovering isn’t really that necessary so I have to hoover every single time I visit... sigh!
But I love my friends! Unfortunately they never visit me, as I’m the furthest and that seems to be the rule, people nearest London don’t visit anyone else apparently. 
in my lovely big clean home. And I’m not even allowed in one friends kitchen, as it’s so bad yet I do eat whatever she cooks and touch wood, no illness yet.
You can’t say anything, even indirectly. This is just how your friend is OP. You can see her outside the house as much as you can.
However my friends are absolute gold dust to me, and so is my mother. They enrich my life so much that I just ignore the dirt. And I even have to stay over as they are so far from me!
Although I admit one friend, that I do love, but was just so casual about ‘my kids got nits’ etc and if I visited my kids would always pick up something, that I stopped visiting. She was also incredibly posh and like some of my other posh friends, had no sense of infection and illness control! I do think lower class people have a better idea of cleaning to not pass on infections etc - passed down through generations.
Mind you, see the other thread on taking off shoes! Bonkers.