I'm guessing she had the sudden realization that she has indeed changed, which brought her happiness (hence her apparent tears of joy). Apparently Kafka and the Trailblazer are destined to change one another; and achieving such change is one of Kafka's main goals.
Not traced. Kafka's legs and feet are on different poses than Asta's. If anything this reminds me more of the one by hinagi #6297394 which still isn't traced.