Very true! She knew him but she couldn't kill him until she had his name, which is the reverse of how the Faceless Men operate. Awesome catch.
I had a thought regarding the title "Mockingbird". Mockingbirds mimic the songs of other birds. If I'm correct (and please correct me if I'm wrong), mockingbirds have no songs of their own, they only mimic others'. This is quite significant if you look at Sansa: She tells people what she thinks they want to hear, rather than her own "song". She's been referred to as "little dove" and "little bird" many times, and many speculate that she could be Littlefinger's downfall (she grows in skill at these games of thrones, while he is likely to underestimate her). She could in fact take over Petyr as Westeros' resident mockingbird.
Fan: "Why do you keep killing off all the characters I love?!"
George: "Perhaps you love the wrong characters."