Patisserie Valerie in Soho has loads of exciting cake, I'm sure they'll do a nice cheesecake.
Used to speak to these guys a lot through work:
http://www.cheesecake.co.uk/home.html
I think they supply a few places in London.
There is also a cheesecake factory in seattle, so awesome, it took me about an hour to pick which one i wanted.. then 5min to feel sick from eating too much.
ps if she has a cheese cake fettish, buy loads from tesco and fill your bath with them, get in, no spoons.
let me get this right a cake made of cheese, cheese and cake together its just wrong