Thanks, Reinhard - another mystery (partially) solved.

Kathleen Tardif appears in the 1901 Census, aged 23. She was born and lived on Guernsey, which may explain the French surname; she was appointed secretary of the Guernsey branch of the RSPB in 1918. That's all Google has to say, though. I wonder how that poem caught the eye of the anthologist[s], and whether she wrote anything else.

Also, what Blandiver said. I defy anyone to look at that picture and not marvel. O fair she was to look on...