Is the lump on her nipple itself? Might just be a case of an "infected" hair follicle on her tummy (a pimple) that has gotten bigger over time.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge