She protected the villagers from Chou Shinra Tensei which would be extreme gravitational powers and since she said nothing to the effect of that was close or I thought I might die from that we can reason that she wasn't expressly disturbed by the gravitational force being put upon her. The state of being clothes, and the state of being in clothes are entirely different principles. Naruto was in clothes yet he was burnt.
She took Shinra Tensei from a long, long distance away before. As in, Pein was flying over the village, she was hundreds and hundreds of meters away, and there were many objects in the way to buffer the blast. The time she is sitting snuggly in Naruto's jacket the chakra cloak takes Shinra Tensei from 2 inches away. That's a pretty huge difference. If Pein had used his village destroying blast on Katsuyu from 2 feet away, I doubt there would be much left of her to scrape off the pavement. She also got sucked into Planetary Destruction, an even more powerful tech... so yeh, there's that too.
Look "Mr Harvard", you don't have evidence the cloak touched her, so you can't claim it as a feat. You're also ruining the credibility of people backing Tsunade, by making such a ridiculous claim- "his clothes are plot no jutsu invincible... and she was hiding in his clothes... but she took the full force and his clothes took none" is a laughable argument, especially when you can't prove it. If we were meant to believe that Katsuyu survived a huge ordeal (as opposed to being safely protected behind the chakra cloak) we'd at least she ripped clothes (they can still manage that in the manga without making this porn). Instead there's completely unscathed. The evidence just isn't there.