So this was an interaction that came up.
We ruled it as Jaina's Light cannot shoot through the dust field is not treated as obstructed, but rather the dust field simply does not allow you to shoot through it.
I'm certain this is how to correctly do it, but I did realize that the RRG says if you trace LOS through an obstacle (dust field), the attack is obstructed. But dust fields text overrules it and prevents any attack.