if leblanc uses mirror image on my unite and i react with retreat to remove my unit, does she still get a 0 might reflection which they can play and conq with?

Yes. Retreat resolves first and puts your unit in your hand, so when Mirror Image resolves the "becomes a copy" instruction simply fails (Rule 359.3.e.6 — instructions that can't be followed are ignored), but the token is still played to LeBlanc's base as a 0 [M] Reflection with Temporary (FAQ #9729, #11492).

And yes, that token can still be used to conquer: it enters ready, so its controller can Standard Move it from base to a battlefield during their Main Phase, and a unit doesn't need Might to conquer an empty battlefield (Rules 144, 187.3, 446). Just be aware it has Temporary — it's killed at the start of its controller's next Beginning Phase, before scoring — so it has to be used that same turn, and conquering with it only scores that battlefield (Final Point still requires scoring every other battlefield that turn).