Shortly after you begin the fight, you'll receive a red message, "Queen Dulseris summons forth protectors, you may be able to put the barriers back up to keep them at bay!" Click the three seashells quickly to open them and rebuild the barrier.
If you are too slow with the shells, x4 Royal Protectors will add. If that happens, just revive, then /togglemerc to re-summon Vishra.
When the barriers are up, kill the queen.
Gather the gem at ( -99, 7, -866 ) /waypoint -99, 7, -866.