The thing about Sublime Grace of Mela is that it doesn't provide much of an immediate benefit. Moon can learn Solar-level Air Aspect charms, but she won't start with any and will need months to learn a significant number. It's more suited to spending a couple of months in the Sundial Throne than fighting a war and attempting to manage an Empire. Both tasks at which she will be substantially better at soon.
The same reasons that a civil war would have prevented Anys Syn from using her Hessiah persona will apply to Moon and Mela. Her guise may be more compelling, but that doesn't really matter when the other side simply ignores her or tries to kill her. In peace, however, she could achieve a considerable following through her grace, power, wisdom, and potent training effects.
Beyond all that, Mela provides an excellent excuse for skipping out on the invitation.
