She wants to give him something
She was sitting next to him, expressing her concern about the situation they were in, when Matt launched himself on top of her.
"Ah..." A soft gasp came out of her mouth in surprise, but suddenly, her lips were sealed again.
Those currents of energy that the books mentioned you felt when your loved one kissed you crossed Isla's body, causing her to fall completely into Matt's arms. She didn't need to resist; she just needed to accept this reward he was giving her.
Although she didn't understand the motives, it was enough that he was doing it. So she enjoyed the moment as their hands intertwined, bringing extra illumination to the room.
That beautiful moment lasted for a couple of minutes until Isla felt suffocated. She had no experience kissing, so she tried to catch her breath and continue, but Matt ended the moment as he watched her.