Due to some circumstances we weren't able to do progress for a couple of weeks, but tonight we finally got the chance to go in and give Grand Magistrix a try - and down she went! Gul'dan - you're next!
(We also killed Botanist two weeks ago, but since I was absent I have no screenshot to share of that kill.)
After some unsuccessful attempts on Heroic Tichondrius, we decided to regroup and try something different. Approaching Spellblade Aluriel we tried a couple of different approaches, and eventually it clicked - and down she went!