Important Note: I will be live-streaming my run for Server First Engineering tonight starting at 12:45 AM Mountain time (long live Mountain time, the time zone no one uses!) and I invite you to hang out at twitch.tv/faidtastic to see just how much it ends up costing me!
A reader, Groo, sent me an email a while back that I was far too slow to respond to. However, we still have a few hours for the non-EU folks. (Sorry, EU friends!)
With the destruction of Theramore a lot of NPCs have disappeared including Helenia Olden. I was not able to find any information about a relocation of her or her wares. (Please share in the comments if you've spotted anything that's gone missing!)
While no recipe in the game is 100% specific to Helenia she is the only Alliance vendor available for a few items. Luckily it's not too late. If you have any character that hasn't yet done the Theramore event you can head out there and it won't be cratered quite yet. Since mages can port you straight there you can even roll a new alt just to snag her items if you already did the event on every character.
Be sure to pay her a last minute visit and buy her limited quantity recipes Design: Truesilver Crab and Design: Black Pearl Panther. Once she disappears players will need to look to the Horde for these recipes.
You can also get her cooking recipes and Pattern: Murloc Scale Bracers but as these items will still be available on other Alliance vendors they're lower on the priority list.