Sol won't activate with attacks from 2 range by anything that isn't a bow. Staves can't trigger it either.
It's the same with the other masteries. Deadeye will activate from wherever, since it's the Marksman mastery and they use bows. Stun and Colossus won't activate from 2 range, Flare and Corona won't activate with staves (that last is obvious if you think about it), et cetera.
So yeah, Mist's not triggering Sol unless she's using a sword from 1 range. And if you're letting that happen, you're going to want Sol to activate a lot.
Yet another reason why Mist should never be used as a combat unit in FE10. As such, do it. It's the essence of self-imposed challenges in Fire Emblem and if you do it enough you'll be cool here.
Five dots, bitches.