I guess using something negative and borderline painful to motivate you to be at your best- is an approach I would rather avoid personally.
It just appears, to me, as a rather dark pattern of thought or mentality to subscribe to. I'd even go as far as saying it is machoistic.
Like you said , you both love each other so that means she most likely isn't thinking about her ex's penis; but you are- why give him that victory?