That was all she needed to do to activate the spells; the magic swept across her, making her shiver as her fur stood on end. Her whole body seemed to shrink at once, compressing down from her impressive six and a half feet in height to a far more normal five foot four. The extra mass didn’t vanish though, it spread out around her body. Her ass filled out, lifting her in her seat, while at the same time inches were added to her breasts, swelling them from merely large to truly massive. Even her nipples grew larger, becoming the thick, fat tits of a mare who had once nursed foals.

Conservation of mass, I like it.

There's definitely something Trollestia about this whole thing she's got going-- transmuting herself into a form for going incognito, designed so that she can and does turn right around and impersonate herself as part of her fun.