Student film, no pay, but the director just got into Sundance

OK so I know the default answer here is "never work for free." But hear me out. A friend forwarded me a casting call for a thesis short at USC. No pay, 2 shooting days, 8-hour days with meals. Standard student film stuff, I'd normally pass. But the director's previous short just got accepted to Sundance. Like, actually Sundance, not some random festival. She's also repped by WME already. The role is small — maybe 15 lines — but it's the emotional core of a scene that could be a really strong reel clip. My gut says the connection alone could be worth it. But my wallet says I turned down a $400/day gig last week and now I'm considering working for free? Am I being smart or being a sucker?