Your dog needs to be stopped BEFORE she gets completely adrenalized by the situation....which means someone has to be with her and watch her, and call her away from the fence or distract her from the shadows BEFORE she gets far into the behavior. That's work. If you're talking about using an e-collar set to stun in order to stop behaviors she is already engaged in, then use of an e-collar is likely to make her more neurotic. Plus she is likely to make the wrong association, and you can create a dog aggression issue if she associates the stim with the approaching dog.
--Regina and the GSDs:
UCDX von Sontausen Holy Grail (The BUNNY!) HGH, UD,RA,BN,GN, ASCA UD RAX High in Trial
PAM Monster Mike SchH2,UDX,OM1,TD,RE,VER
PAM FGDCh Ianna von Sontausen UDX,BH,TD,RE,PT (4.26.1998 - 2.11.2013)