Anthony Carter quotes a book quoting Luther on what Mary was doing when the angel appeared to her (Luke 1:26-33):
Yes, during prayer and other spiritual exercises, but contemplate that second sentence for awhile. It’s when we are fulfilling our vocations–as spouse, parent, citizen, worker–that angels “prefer” to come to us and that God works with and through us most powerfully.
Quite possibly Mary was doing the housework when the angel Gabriel came to her. Angels prefer to come to people as they are fulfilling their calling and discharging their office. The angel appeared to the shepherds as they were watching their flocks, to Gideon as he was threshing the grain, to Samson’s mother as she sat in the field. Possibly, however, the Virgin Mary, who was very religious, was in a corner praying for the redemption of Israel. During prayer, also, the angels are wont to appear (from Come Thou Long-Expected Jesus, ed., Nancy Guthrie).