My raiding experience is not extensive, but I have never encountered a fight in WoW as interesting as Priestess Delrissa and her adds. The mobs that compose this fight appear to lack traditional aggro tables. The result is a very chaotic and fun fight, where you could be alone one minute and double-teamed the next. I have done this fight 3 times without success (probably due to a lack of crowd control classes). For a druid, the challenge here is to offer some meaningful contribution to the group. This is a rare occasion for a druid to perform many roles, none of them well, and save the day.
Feral Druids have some decisions to make before this fight. The strategy of the druid can be to outlive the random attacks (bear form) or help to heal as needed with interspersed DPS, hoping to keep HoTs on oneself or heals from the main healer. Certainly, performing a timely Combat Rez or Innervate can make a big difference. A nice: /cast Barkskin; /cast Tranquility can also be very helpful, so ask your group to keep tight- when they aren't the victim of NPC Fear.
The problem with the Bear Form strategy, is that your bear is not adding meaningful dps or really maintaining aggro. The benefit is that you will likely be last to need heals if you don't get swarmed with casters (my guess is that no single person can aggro more than 2-3 mobs simultaneously). Overall, this seems the worst option to me.
Alternatively, a feral druid can attempt Cat form with emphasis on DoTs being maintained to keep the DPS rolling while feared or otherwise CC'd by the mobs. Either way, a PvP set is very nice for this encounter. The difference between my bear gear and DPS gear is >3000 health and there is no crit protection in Cat form/gear. Cat form with tank gear on will offer some improved survivability, but not as much as burning down mobs with DPS before they can become a problem. DPS in this gear is terrible. I found myself dying in my pure DPS gear VERY quickly.
Unfortunately, we lack good CC in this indoor setting, but that shouldn't cause you to balk at throwing Cyclone around freely and frequently.
This fight is a very nice departure from tank'n'spank, run when (insert voiceover/enrage graphic) fights that typify instances. Hats off to Blizz on this one.
In summary, a Feral Druid's best chance in the Lady D fight is to equip melee pvp gear, stock up on stamina buffs and try to DPS that lady down in cat and if able throw out some heals and cyclone.