Janet is a seriously loaded alchemy merchant based in Arcadia's Cauldron in Whiterun. Not coincidentally, she is also Arcadia's daughter, and she carries large quantities of most alchemical goods. In fact, it's a wonder she hasn't put her mom out of business. You can usually find her on the second floor.

Note:
I originally created this vendor to offset a certain weapon mod, which I thought had prohibitively high crafting requirements. Many players might consider Janet's inventory and gold reserves unbalanced.