Met a WG last month in Scotland who had the exact same experience with the same type of stainless steel plug. Trouble is, the base is too narrow.
She said she was so terrified/embarrassed about going to A&E, that she told the client he had to get it out. Eventually he came up with the idea of locating the thing by feeling for it through her vagina, which he did, then manipulated it down and out. Caused a lot of bleeding, but no long term damage.