“I was the best of those sons of bitches! The most loyal! Not even Alastair knew! Only Lilith” – Ruby, 4.22
I know that Lilith and Ruby’s relationship was not really shown at all in the show but I can really image these two ladies plotting to release Lucifer from Hell, and thinking of ways to lure Sam into drinking demon blood and becoming a vessel. They are both such strong characters who sacrificed so much for their end game; Ruby got close to Sam resulting in many demons believing her to be a traitor of Hell and Lilith gave her life in order to open Lucifer’s cage (and then Ruby also gets killed a few minutes later). Even though you don’t really see them together, I do believe that they had a very close friendship.