On Shabbos, may I ask/hint to a non-Jewish housemaid to take frozen milk and put it in hot water (from the urn)?
Yes, you may tell her to do it, as long as the milk (bottle) will not be totally covered in the water. See here for a similar case: https://asktherav.com/2763-can-we-take-water-from-our-shabbos-kettle-to-warm-a-baby-bottle-in-a-paper-kli-shlishi/…
