There have been a number of discussions about Russian literature and translation in general
http://www.online-literature.com/for...d.php?t=14658&
and Garnett in particular here:
http://www.online-literature.com/for...ad.php?t=31955
of which I won't repeat myself again
http://www.online-literature.com/for...99&postcount=3
except to say that she did learn Russian and had many Russian revolutionary friends who visited her in England, or who she visited in Russia, including Tolstoy who praised her work on translating his novels.