A couple of things:
If you're playing on Relentless, be joyful, you never had a hope to start with. Relentless will spawn an AV no matter what team size.
If you're not on Relentless and having trouble bashing the EB version, give me a shout. I'm on most nights as Seethe these days. 
Yrah I managed to complete it lastnight. As you stated I had my level set at Relentless so it was tehrefore spawning an AV. Not a bleedin chance 
Reset my level down a couple of notches and managed to do ti no problem.
Hi all,
Ok having just reached lvl 40 with my Robotics Mastermind I decided to go pick my Patron. Having done a few missions for him he has now asked me to recruit Silver Mantis. Have made it all the way to the end where she is but I'll be damned if I can beat her with just my bots and myself
So heres a plea to you all to see if any of you are interested in teaming up to beat her.