Tannysa is a Herbalism trainer located in the Mage Quarter of Stormwind City.
In-game Picture
Location in Stormwind City
She is standing outside the alchemy shop Alchemy Needs.
Coordinates: 44.4, 77.8
If you are using the TomTom addon, then you can use this command:
/way Stormwind City 44.4 77.8 Tannysa