Best thing to bolster immune for someone that can't exercise

I have a friend who has hip arthritis and other such mobility-related impairments and therefore cannot exercise (or at least she feels she can't and that it would set off her pain). Therefore, she doesnt' even get out and walk.

Her diet isn't that great (although she would swear to high heaven it was & has when I've confronted her about it. LOL)
So what can she do to bolster her immune, without exercising? She's a very sickly person, she and her kids are getting sick very frequently.  She says she's tired of getting sick, and I'M tired of SEEING her & her kids sick! LOL Shes unemployed, and her frequent illness is a reason why she doesnt' want to get a job since she's afraid she'll get fired for constantly being out sick!

Any suggestions?

[Dallasfan]

Yes she is headed for more problems. I am glad she has a good caring friend like yourself. Even severe arthritis patients can exercise if even only passive range of motion exercises from a seated position. Have her get on a good healthy diet, stop smoking, and see her Doctor for more advice. She may need counselling if she is depressed. Have her become more active in the faith of her choice. A good positive attitude can indeed  "boost the immune system ".  Keep being her friend..she needs you.