Does kneeling to attack with Wicked Seductress allow the attacker to use her response before defenders are chosen? We've been playing that she can do this, but the phrase "is knelt" kind-of sounds like she has to be knelt by some other effect.

Bray said:

You and your friends have been playing the card correctly.

Whenever a card kneels it is also considered to have been knelt. Therefore, an attacker kneeling her to participate in a challenge would be able to trigger her response. Since there are no other immediate framework actions after attackers are declared, her ability would have to be triggered immediately after she is knelt, which is before player actions and the framework actions of declaring stealth and then declaring defenders.