If you're not going for the Lord of Hollows ending, play through Anri's quest until you meet them in the Church of Yorshka (that just involves talking to them in two places in the Catacombs and NOT telling them that Horace is alive in Smouldering Lake you don't even have to kill Horace so long as you don't tell them Horace is down there). You'll be able to buy the set afterwards. If you're going for the Lord of Hollows ending, complete the marriage. (For example, my Luck build uses Anri's Straight Sword as her primary weapon, so I just killed Anri and Horace at the Halfway Fortress so I could get that weapon right away.) Straight-up murder them when you encounter them in the world at any point. Anri has to die to let you buy the armor set from the Handmaid, but that can be accomplished in any one of a number of ways:
