If an artist has bad health to the point they can no longer perform or record, then that would be stupid because both the performances and songs would be absolutely awful. An artist has to look good, and sound/look fairly healthy in order to be presentable. Def Jam let her take time off & vacation this year anyway.
She sells a lot everytime - she's certainly more in a position to take a break than other artists, but clearly she herself doesn't want to take a long break. During TTT she talked about how hard she worked & yet here she is again releasing in Nov. Therefore, I think she simply likes working constantly, & I'm sure her label does too.
