Experimental Potion: Test Subjects Needed

[npc=110642] is in the Alchemist Lab The Underbelly at 75.8, 83.2 (south-east on the map),
she offers you Experimental Potion: Test Subjects Needed which will transform you into a
various creatures granting different Experimental Potion buffs for 20 minutes.
Buff persists through death and is working only in The Underbelly.
Quest reward is 150 [currency=1149].
You will be transformed into one of the following creatures:

• 
  
• Skrog
  Transform you into a skrog when you are in a space that is large enough to contain one.
  While transformed, your health and damage are tripled.
  https://www.youtube.com/watch?v=h_7Xguo7ulw
  
• 
  
• Nightfallen
  For casters receiving fatal damage will instead transform you into a withered.
  For melee transformed into a nightborne. Haste increased by 10%.
  https://www.youtube.com/watch?v=tTjtv1PU1Hw
• 
  
• Tuskarr
  You can fish Sightless Eyes from open water in the Underbelly.
  https://www.youtube.com/watch?v=DojJayxcCk8
  
• 
  
• Kobold
  You can collect candles from the corpses of your enemies in the Dalaran Underbelly.
  
• 
  
• Harpy
  While within The Underbelly, you can fly for short periods of time.
  https://www.youtube.com/watch?v=gMJ-LjfIdLg
• 
  
• Dryad
  You can use the [spell=219734] ability.
  
• 
  

Be careful The Underbelly is a PvP zone. When you enter Underbelly you get [spell=192229] or [spell=192221] debuff.

• 
  
• [spell=192229] means the guards are on their posts and no PvP is allowed.
• 
  
• [spell=192221] means there is no guards and Underbelly becomes free for all PvP zone.
  During that time you can farm Sightless Eyes by killing other players.
  You get from 15 to 50 [currency=1149] for each kill.
  Guard Captain [npc=97359] is the one controlling the guards.
  You can bribe him to call off guards or call them back for 50 [currency=1149].
  You can hire personal guard [spell=203894] if guards are not on their posts for 5 gold and you'll not be flagged for PvP,
  so do it if you want to avoid ganking.
• 
  

I've now done this quest and been turned into a dryad 5 times today. Does anyone know what triggers it to be available? I thought it was every 2-3 days as I hadn't noticed it often, but today just keeps on offering it.

Does anyone know as of 7.2.5, what the trigger is for her quest to appear? Havent seen it up in days.