And for those that don't recognize her modern name, this is Cassandra Peverell - AKA The Harpy. :)
Also, definitely metal caps. It will be used in the construction of either the shower or workshop. Directly from the Pinkastus Estates page:
We need bottlecaps, especially twist off caps or pry off caps that are not too badly bent. We're thinking of incorporating them into the workshop (maybe the shower). If you are at a party with many a bottle being opened, especially you Lilies goers and party throwers, and you happen to think of us, we'll take whatever you choose to save for us with much gratitude!