A level-nine bard in my party recently joined the Conclave. She was given a welcome package by a voda (who they've helped many times throughout the campaign) that included a Selesnya Guild Signet, several charms, and a sacred clipping from Vitu-Ghazi so that the World Tree will be with them wherever they go. Mechanically, it's a focus that doubles as a material component for several spells.

Since your relevant player character is a druid, they could briefly commune with Mat-Selesnya in some way that may heighten their status in the guild. I'd also try to make use of existing NPCs with whom they may have some familiarity, like Trostani, Emmara Tandris, etc. Otherwise, I'd work with the character's backstory to somehow advance whatever their arc is.