I think it is appropriate to say that the VQ isn't totally invincible, as no units are.
However, while we can compare her to other near-invincible SC's and we can point out the few, specific counter-measures, she is still immortal, on top of all the rest. So yes, if you are playing the right race or have an SC designed to defeat her and you have researched the specific paths or created all the right items, you can *maybe* beat her in a given encounter.
Your victory forces her to re-spawn. As I see it, that's just an extra ability, a free "Returning"
- Kel