Die Walkure, Act 3 from the BBC Prom August 14, 2007 Youtube link.
Who is the blond singer in a black dress?
I’d like to see if she has any recordings.
I’m pretty certain that the actual performance featured in the video is this one from 2005:
The same (or similar) cast were also at the Royal Opera House for a run:
http://www.thestage.co.uk/reviews/review.php/8648/die-walkure
Judging by the cast list in the second link I reckon that the singer you are looking for is Rebecca de Pont Davies:
http://www.robert-gilder.com/ArtistDetail.aspx?artist_id=2311&category_id=1010&location_id=3002
Many thanks, Struan!
I love the 'Dope.