Reflective Shield is currently quite a bad card, as it is too risky to play cost–wise because of it's requirement for prediction, even more so than the 6–Cost Mass Death, and this comparison also brings out the question of what it's cost should be, relatively speaking.
My first suggestion is to simply reduce it's cost to 5. It's pretty similar in efficiency as compared to Winds of War. Damage dealt would be slightly less than 5 on average (since the average Power of attackers seldom reaches 10) and it is less flexible in terms of Zones it can affect, balancing out the damage reduction to your Fortress for a turn and not affecting your own characters.
My second suggestion is to turn it into an Artifact, following the concept of Low Orbit Ion Cannon by including 'exhaust for 2 turns' as part of its activation cost and Unique status to prevent spamming. Its original cost could be 4, and its activation cost could be 3 (not because I think that it is on par with Ion Cannon, but because I think Ion Cannon is too cheap for what it does).