He knew what he was doing. Did he feel bad? Sure. Definitely, in fact, but Lorca is the ultimate pragmatist, and pragmatic strategist. He was trying to dissuade her from the moment she came on board, using all the tools. He likely succeeded, or at least made for a good delaying action.Shhh, this is the "Lorca doesn't get the benefit of the doubt" thread. He knew exactly what was going to happen to her, because he's, I don't know, a psychic. And evil. Evil psychic.
Then he messed up, and set her off. He resorts to begging, searching for sympathy. No dice, but fortune lands in his lap again, and Lorca is not a wasteful man. Sarek is too ill. "Well, aren't we lucky we have this Admiral aboard?"
Admiral? didn't they specifically not want Starfleet at this peace talk? She goes anyway, apparently in a shuttle with no back up. I'd like to assume she knows this is all wrong. She says to Lorca "When I get back..." She doesn't want to take his ship away. If she did, she could have done it then. No, she wants the delaying action, too. The admiral is aware of the truth, but loathes the ugly part of taking action, and following through on what she now knows/feels to be necessary.
And then witness the proof of all this, that the writers toss in our own laps, when Lorca gets the news that she's been captured by these barbaric monsters; the same monsters that he killed his own crew over in order to save them from.