Thank you everyone, you've been really helpful and sorry about the download - many thanks Jim!
I think you might have helped solve the mystery. In answer to a couple of queries, the photograph is actually (unfortunately) stuck to the back of a piece of cardboard - it's extremely thin though and doesn't feel like a 'proper' photograph. The Kedleston link is through my great grandfather who was a blacksmith at Kedleston in the late 1800s / early 1900s. The family story is that all the staff were given copies of the photo.
I found the parish records for Kedleston around 1890. There are three possibilities for Lord Curzon's daughters' marriages - Geraldine (1901), Margaret (1899) but I believe the photo is of Eveline Mary Curzon, who married Sir James Percy Miller, 2nd Baronet Manderston, in the chapel in the grounds that STG mentioned in 1893. I found a photo of the groom online and they look similar and also found a newspaper archive that describes the dress almost exactly. Apparently she was very popular in the village which may explain why the staff were given copies? I'm going to get in touch with the Kedleston archivist to see if any of this fits. If it's not her I'll look into the other daughters.
So many thanks to you all once again for replying and pointing me in the right direction. You've been great

Lou