Even if she was sick - though I agree it's a rather baseless assumption - why does the show need to address it? Why does the whole world need to know about her health status in order to enjoy her work? Such entitlement.
View attachment 12922 And meanwhile no one mentions her obviously overweight friend. Such double standards when it comes to attacking a thin girl vs someone who needs to take pointers from her.
So I suppose that if Stranger Things suddenly feels the need to create a sub-plot surrounding Nancy's weight, it should involve her friend, too. "Barb the Lunchtime Bully."