Macha can ignore and hit through the 10 second invincibility buff one receives while transforming.
As you can see in this video, I transform, gain the buff, but Macha still hits through
… (more)it. I tested this on Dullahan as well, and he doesn't ignore the invincible buff, so it seems that this is isolated with Macha.

I'm not sure if this is character specific, or if it has anything to do with the fact that I skip the transformation cutscene with FI. I'll have to test tomorrow and see if she can hit you through the regular transformation cutscene as well. Anyone else experiencing this?
EDIT: Confirmed that even when transforming the normal way, she can still damage you. You are invincible during the cut-scene portion, but can still be hit during the 3-4 leftover seconds after the scene finishes. (less)