So basically, the magical girl through magic fills herself with lunar energy that leads to a werewolf transformation, and then the ribbons that turns into clothes part comes in to complete the magical girl transformation? Personally, i would see a magical werewolf being naturally more colorfully flashy than a regular werewolf, like having parts of their body of different color, some tattoos, a halo, etc.
Btw, i think it could be also interesting if the magical girl ends up on a partial transformation, to still keep their consciouness on but slighty struggling against her instincts but if the villain pushes her over the edge, she loses control and fully transforms into a magical werewolf.