Kisara’s battles
Rewatching Episode 207 and 208, I believe there are two reasons that Kisara didn’t summoned the BEWD despite being able to do so of her own free will (unlike in the manga).
Reason #1: she was testing Seto
When she was dragged into a Ka battle, she turned to Seto for assistance, hoping he would help her get out of this bad situation like he had done all these years ago (at the cost of his village and his mother).
Reason #2: lack of experience in Ka battle
Until that moment, she had never fought another Ka before, especially not in such life-threatening conditions. Of course she (and anybody really) would feel at a loss for what to do in her position. That was why she needed Seto to help her for he knew better than her about this kind of fight. After seeing him duel with his Ka (and both figuratively and literally stuck in a bad position after that), she stepped in to defeat the second opponent.
And in Episode 214, the second time she was facing another Ka with the intention to hurt her (boyfriend)…
she fearlessly summoned her dragon and fought back!
At the beginning of the the first battle, Kisara displayed a certain level of wariness of people, even to Seto who had once saved her life (probably thinking he might not help the person supposedly responsible for the destruction of his village), until proven otherwise. In the second, she now had the knowledge of who was on her side and who was against her (and / or her loved one), and the experience of Ka battles. Both contributed to her will to fight (to protect).
While her character development is not as prominent as Yuugi or Kaiba, it is there.
