...recommendations from my sis: 
  
"well Le Manoir obviously very good food and location all round. If rich, they can stay there too! 
  
Other Michelin starred places (around general area of Oxford but not in Oxford itself): 
The Nut Tree, Murcott 
The Goose Restaurant, Britwell Salome 
Charles Napier, Chinnor (hard to find!) 
Vanilla Pod, Marlow (not been for ages) 
Hand and Flowers, Marlow (not tested) 
  
In Oxford: 
Brown's is quite traditional to Oxford but just a good brasserie really 
Gee's restaurant, Banbury Road 
Malmaison quite good, again good brasserie but good building/hotel cos old prison (the one Porridge and original Italian Job filmed in!)" 
  
Hope that helps