Where magical girls cross over with henshin and especially sentai, there is usually meaning to the magical form. How tied this is to any specific emotional or character beat varies greatly from series to series. In precure, uh... which one? Precure has done everything. There are over two thousand episodes of various precure shows to pick from. That's a low estimate, it might be over five thousand. It's probably not OVER EIGHT THOUSAND, yet.
In Lyrical Nanoha, the characters' personalities and their magic definitely reflect each other, but on a symbolic Doylist story level more than from a diegetic Watsonian perspective. This contrasts Sailor Moon where the magic works on the original friendship is magic rule, predating My Little Pony using that as a central trope. Also on the divine right of moon queens but ehhhh....
I would say that all transformations (henshin) in heroes and heroines who go through them to assume their heroic identity reflect an iconic role and totemic personification. Sometimes this reflects the inner personality, whether flaws (Madoka Magica, for reasons discussed by @soleilraine), or the ideals embodied, or just favorite snacks (there are a LOT of precure shows). Sometimes the forms reflect something larger and beyond the girls themselves, although the girls tend to have congruent personalities with the type in most cases - magic knights rayearth, for example, or She-Ra.