Hiya, being an ex londoner I did a google search for you and found this really helpful site.
https://www.google.co.uk/hotels/?gl=...;ph=0;si=;av=r The beauty of this site is that you can book her accommodation for her online, I assume you know her budget and what she would like so enjoy, I do hope she has a wonderful stopover in our Capital city as there is so much to see.