I'll be staying at The Carlton Tower Hotel on Cadogan Place.
I will be working most of the time, but my sister will be solo sightseeing during the day.
She has decided to do a full day tour and then will probably wing it the rest of the time.
Is there any cool 'off the beaten path' things. She likes open air markets and people watching.
Unfortunately we will not be in London over the weekend, just in Monday, out Friday.
Any thoughts?

Your sister might enjoy either a 2 hr guided walk with London Walks or they also do a full Explorer Day which includes the train trip and a guided walk. The Explorer Days go to places like Cambridge, Bath, Canterbury etc. We have done about 6 of their guided walks and think they are fantastic - good value and you always learn something you didn't know. You don't have to prebook the walks, just turn up at the designated place and pay the guide.
www.walks.com

Borough Market is open Fridays, it's food only but great for a look, even if you don't buy much. Southwark Cathedral is next door and worth a look. There is an old fashioned tearoom nearby
http://www.teaandcoffeemuseum.co.uk/index.html
You don't have to pay to go into the museum if you just want a cup of tea, it's optional.

Kay

I second the London Walks idea - particularly if you are short on time...I did a Little Venice walk which is a great area in London. I also did Hampstead-Heath which is a really pretty area...

Definitely hit some pubs!

And of course, you have to see some of the tourist highlights - Westminster Abbey, Tower of London, London Bridge, etc. I did the London Eye which was cool, but you can skip that...

Here's our trip report from last year; it may give you a few ideas.

http://www.fodors.com/forums/threads...p;tid=35015831

Lee Ann

Here's my trip report from last year, where I did mostly "off the beaten path" stuff by myself:
http://www.fodors.com/forums/threads...p;tid=35064483

Also, I third the suggestion of London Walks.

I just returned from London and will top my report for you. I highly recommend using London Walks.

Excellent information. I am so jealous that I will not have much time to explore with her... but then again, touring London alone will be pretty cool for her!
Thanks so much

she has to hit the V&A, Libertys and the shops/area below the OxO tower

...yup...I have advice...

Bring lots of money.

The highlights from my trip were: Soane Museum, Cabinet War Rooms, Verger's Tour at Westminster, and the best...the closing ceremony at the tower (Ceremony of the Keys).