Hotels I have stayed at and enjoyed in London (generally on business but would be good for private usage) include;
Crowne Plaza St James (Near to Buck-ham Palace and Knightsbridge)
http://www.ihg.com/crowneplaza/hotels/us...-_-GBEN-_-lonsj Hotel Indigo Paddington (somewhat north of main shopping area but good for tube and trains) Modern reasonable price but quite small rooms.
http://www.indigopaddington.com/The Sheraton Park Lane is central and a nice hotel if slightly expensive.
http://www.sheratonparklane.com/For enjoyment I would recommend a few less common stores rather than Harrods and the usual range.
Shopping with

Liberty Store, just off Regent Street.
http://www.liberty.co.uk/ I think this might be of interest to your better half given the soft fabrics/clothing and history.
https://plus.google.com/101595234785514851091/about?gl=uk&hl=en remove all plastic cards before entering.
Rather than Harrods I would recommend Harvey Nichols nearby it.
http://www.harveynichols.com/http://goo.gl/maps/7b8xi - Great Café and Wine store on the top floor.
Great Italian Food for dinner just around the corner – medium price by London standards.
http://www.signorsassi.co.uk/ -
http://goo.gl/maps/ChZzI French Food and an amazing building
http://www.bibendum.co.uk/ (this was the old Michelin building and has a food hall as well) This is around the back of Harrods and HarveyNic’s.
http://goo.gl/maps/owxo8 Again not cheap.
There is a new building that has just been completed which is called “The Shard” which should have an open viewing deck now. Great view of London. (London Bridge Tube)
http://www.theviewfromtheshard.com/ HTH