Ornifex in Dark Souls 2 not appearing

I've tested killing several important NPCs such as merchants and I have seen that they "come back" as tombstones after a few "real world" hours. The same applies to Ornifex, her tombstone will appear in her prison cell when killed. I believe the amount of souls you need to trade with her is 11,000 souls.

In any case, if the tombstone is not there after a few hours or even restarting the console and the game, I don't think you'll have any other option than to start NG+. Alternatively, you could use a Bonfire Ascetic at the nearest Bonfire to force that area alone into NG+; it'll make everything, including any bosses, respawn as NG+ level, but will also respawn all NPCs and most lootables.

The guy in the video is using the Brightbug, the effects are:

• Almost if not doubles attack and splits damage received to about half.
  
• The duration of the effect is 120 seconds, not affected by the Lingering Dragoncrest Ring.
  
• Does not stack with other self buffs.

He may also be using a Ring of Blades, the Lightning Clutch Ring, and the Old Leo Ring. I'm not familiar with the gear he's wearing but I presume there is a reason he is wearing it. Hope that helped!

EDIT:

He is using these items:

• Flower Skirt +10 (+2 VGR, +1 END)
  
• Crown of the Sunken King +5 (-1 VGR, -1 VIT, +1 STR, +1 DEX, +1 INT, +1 END, and +1 FTH)
  
• Raw Rapier +10 (highest base damage because scaling is insignificant at sl1)
  
• Ring of Blades +2 (+50 Physical Attack)
  
• Dexterity Ring (+5 Dex)
  
• Flynn's Ring (Grants the user bonus physical attack based on their maximum Equip Load stat)
• Third dragon ring (HP, Stam & Load increase)