"But--" Luna looks to Sansa, then back in the direction of the Cornucopia. She still wants to see if there's anyone left that she can help, but Sansa's presence here changes things. Luna doesn't care much if (when) she dies here, but she has more hope for Sansa. There's a moment of calculation, an unknown number of people she might be able to help versus one she's sure she can, and she takes a quick step towards Sansa in compliance - if still with a hint of hesitation. "You're right, I'm sorry. We should get going."