Your friend is the racist Tracy, obviously one of those people who believes racism can be found in anything if they twist it enough. You had not heard the supposed offending slang term , neither had I but then I'm British, but to claim that using the suffix "itis" (medically speaking, inflammation,) in a colloquial way has racist origins is just race baiting.
I'm reminded of a case in the UK some years ago when leftist activists tried to mount a campaign to force food shops and restaurants to rename 'black pudding' as blood pudding because balck pudding is racist. now black pudding, so called because of its colour has been around since the medieval era so nobody was being racist when they named it.
There was a public outcry, people asked why Boudin Noir, Swartwurst or Salami Negroni were not being attacked in the same way but it was the Caribbean, Muslim and Jewish communities who rode to the rescue. People in the Caribbean community said black pudding was fine with them, a tasty, nutritious and cheap food, not racist in any way, and what they really founf offensive was middle class white people telling them what they should be offended by, while Muslim and Jewish people pointed out that black pudding is made with pig blood and the name distinguished it from other types of blood pudding made with calves’ or sheeps’ blood.
(Blood pudding BTW is a mix of oats, barley, blood, offal, fat and seasonong packed into cured intestine. I for one would not consider my life diminished it all types were banned, but many people love it.)
In UK slang we often say a person has "lazyitis" (self explanatory) or maybe the less obvious "decoritis" (phoned in sick in order to finish some decorating. A doctor I know would sometimes write on medical certivicates "oscillating plumbitis" (swinging the lead," or "haemomensitis" (bloody mindedness.)
The list of ways itis has been used in slang is endless.
Next time this so called friend tells you it's not acceptable to use some perfectly innocent word or phrase, tell her she's nothing but a bansturbator (a person who self pleasures by telling others what they are not allowed to do.