Nena - already a grandma a decade ago - started shaving sometime in the latish 90ies, maybe the armpit hair was graying and dying it darker might have created scenes otherwise only known from former dignitaries of US East Coast cities at inaugurations of landscaping facilities, I dunno.
I don't mind the furry little critters in armpits or on more convex parts of the female anatomy for that matter, not everyone has to look like a porn star at work.