Since Milotic is offensive AV will take effect and makes Milotic slightly harder to take out
You might consider :
Lum Berry - Just in case
Life Orb- On the opposite of an AV a Life Orb will shorten Milotic's lifespan but make her hit harder.
If your Milotic had Marvel Scale Flame Orb would activate it and prevent Toxic or Paralysis however since it has competitive it would be a little useless