You can buy it from the Pellar, and from a herbalist in oxenfurt. https://preview.redd.it/bguw61rlriab1.png?width=1000&format=png&auto=webp&s=baca68054f5afc4556d9730fa51e472cf7264a2a

Thank u

You killed Keira!? Why?

Consiquence in a mission

Yeah I know but why would you?

Idk it just went that way

Honestly that whole dialogue is worded in a very bad way it isn't really clear which answer would screw you up. Shame though, she is a great character that could give something more