The strongest character she ever flash froze was herself. But I mean just from your post it doesn't sound like Luffy has any feats for resisting something that can instantly freeze an entire lake. The only instance of dealing with it you brought up was one where he got frozen. Her ice is also permanent, and she can even make independently functioning constructs out of it (she needs to focus to make them act very intelligently, but they can still follow basic commands), not that that's useful here since it takes her some time.
The difference between breaking those other things and being crushed under an ice meteor would be a matter of leverage. If she does it in a timestop, he's getting crushed without being able to do anything about it, so if he can provably survive getting hit with that much weight, then he needs to be able to lift the entire thing while crushed underneath.
Edit: Looking at the size of her meteor again, we may actually be talking closer to hundreds of thousands of tons. That's basically a small mountain.