Well, somehow it's a bit sad they had to use the same illness. But it helps creating a bond between important characters in the show.
I'm still a little surprised Amanti didn't see it in Serika, after all, she of all people know best what Sharon's illness means. Or maybe with her past experience she can deal part of the emotional shock better, even more since she's not very close to her?
Or Amanti didn't see it, because it makes her "power" less magical...