Matthew looks at Jesus as the Messiah, and as such He is King of the Jews, and in the light of His kingship Mary therefore anoints His head (Matt. 26:7).
John, presents Jesus as the Son of God, and shows Mary anointing His feet. She sees Him traveling through this sandy desert, and is careful that His feet do not lack ointment. In point of fact, it was done to both His head and His feet, but each evangelist records what suits his gospel (John 12:3).
Mary could never forget that He had walked with her in her sorrow. Crushed by the power of death, when Lazarus fell asleep, she had known the sympathy of Jesus in the moment of her deepest sorrow, and she had also seen Him take her brother from the grave. She had learned what His grace could do, and what was His power also. He had walked with her in the moment of her sorrow, and now, in the hour of His sorrow, she is, so to say, walking with Him. The Lord greatly valued her affection, and said wherever the gospel goes, the story of that woman must also go. He will never allow it to be forgotten, that when the world did not want Him, one heart wanted Him above all things else. Happy indeed are you, if you have put Christ before everything.