How would you tell a sibling to stop obsessing over various syndromes and stuff?

So I have this sibling who's a bit odd. She's part of loads of groups she doesn't need to be part of like this week she has restless leg syndrome when she doesn't so she's sat here pretending to have it when she doesn't and tests have proven this.

How would you stop someone obsessing over having various illnesses, fears, syndromes/ diseases and stuff. It's like she wants to be sick or seen as special or something. Not quite sure what to do 🤷