I like this idea, which shouldn't be that shocking, as I wrote it. I might be biased towards it.

Grace can't transform her clothing, but she can transform herself. A mere 2% difference in size for Grace makes her clothing effectively feel 6.25% bigger, which could be enough loosen up what might otherwise be something normally too snug to remove quickly.

I went with Grace shrinking by 5% in the comic for the sake of visuals, but that's actually a bit excessive. At least, I assume it would be. I don't exactly have the means to test this, but that's effectively making her clothing about 16.64% bigger relative to her, which is roughly around 1/6 bigger. Given how much of a difference just an inch or two can make in a waistband's looseness, that at least sounds signficant to me.

Granted, with waistbands, the vertical size difference might not matter that much. I imagine it would matter more for something like the shirt Grace is wearing given the neckline. Transformation math is complicated.