Looks like you're going to end up with shit loads more ratnik

. 'Classic Rock' is actually quite diverse and it's all down to the taste of the individual. Your sister may have already suggested these, but they would be excellent albums to get into if you haven't already done so -
One of the biggest selling albums of all time, Dark Side of the Moon by Pink Floyd
and an all time classic from another of the 'big beasts' of the genre - the fourth Led Zeppelin album (which has a whole range of titles)