I think the seeds were from the superfan who supplied the seed advent gifts...or from which fund it went from, I guess business expenses
it is because mary sees her now for what she is and dares to challenge her, tell her no and ask not so correct questions
on the other hand I believe that steffi is tired of pretending that mary has any talent arranging anything (I wonder how her food tastes like - was the Nigella flower seeds a hint that she should stay in the kitchen?)