Yes, they can, but they use the title 'Dame' instead of 'Sir'. In Britain, the feminine equivalent of a knighthood is Damehood. Anyone in the UK and commonwealth countries has a pre-eminent national contribution in any field of activity, e.g sports, movie, etc can be appointed as 'Dame' or 'Sir'. For the details, check here.

English sailor Ellen MacArthur was appointed as a Dame at the age of 28, which makes her the youngest person to be honored. The honor is awarded for her fastest solo circumnavigation of the globe in 2005.