Actually, as she hasn't listed any medication in her multitude of pills or photographed anything that would affect her immune system, she's actually got a vastly improved immune system compared to most. That's the point of RA and the ilk - it's so super strong and sensitive that it doesn't just zap every virus and bacteria in sight, it does it to the various body systems as well.
You know those people who, in an office or school outbreak of the flu, norovirus, chickenpox, colds, coughs and everything else who are the last ones left standing after everybody else has succumbed? Yep, we're those people. I'm one of those people. On the rare occasion that you do get ill, with an uncontrolled immune response, you can become very unwell, but on the whole, you just don't get sick.
The trade off is that you feel tit for other reasons, but you don't catch much, even when in direct contact with people with infection.
Taking medication (a combination of, not just one) like MTX, Humira, oral steroids, etc, etc, takes your risk of infection down to normal, and if not managed carefully through regular blood tests, can then make you more vulnerable. But she isn't taking any combination of those, as we all know a bunch of deliveries of pen injectors and sharps bins would have got pride of place in the Poundshop Damien Hirst medication tableaux.