First, the vampiress flying only last until the end of her action phase. Not the whole round.
Second, Maim Wing only require a Corporeal creature as target. So either NV is flying or not, she is legal, so the card wont go away.
Third, Maim Wing, unlike condition like Incapacited or Restrained, doesnt prevent to regain Flying trait. So if opponent reveal Maim Wing while you were flying, you will drop to the ground for this round because Maim Wing happened after that you gained Flying. But for next turns, you will gain Flying after Maim Wing effect, so you will be able to freely fly, while being immune to futur Maim Wing since you can only have 1 enchantment with the same name on an object.
I hope my english was good enough to be clear.