I have the same problem with Juno. She is undying affection and 100 happiness (108 usually, but it never stays there of course.) Maybe she doesn't like gardening. I sent her to the Academy to train to, but it would not raise her gardening, even after 30 days in classes.
Gardening is trained randomly daily from being a gardener. Think Mai Lynn has the highest skill outside of captures with it buffed. Dakota starts at I think, 25 gardening skill. What a waste, I sent her to devious tools instead, it's much darker that way. Sadly I cannot interact with her at work. although I take constellation in knowing she's learning something. The only thing more amusing is Eliana as the household floorwalker.
These NPCs and their stories. How much fun creating your own.