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You first meet Poppy during the main story quest "Beast Class" after which her companion quests will pop up in your field guide as you progress the main quest line:

Fire and Vice (Main Quest)
A Dragon Debrief (Side Quest)
Poached Egg (Side Quest)
The Poacher's House Call (Side Quest)
Surprise Meeting (Side Quest)
The Centaur and the Stone (Side Quest)
It's in the Stars (Side Quest)
A Bird in the Hand (Side Quest)
Poppy Blooms (Side Quest)

After completing all of Poppy's companion quests, your achievement should pop!