Based on the theory here (3153161) and on reflection, I thought that the pony Mayor Mare might have an undisclosed relationship with might be miss cake's older brother, who he most likely knew before or might have known after bright mac's marriage and pear butter, and this could bring together the skills of mayor mare with the sweet skills of the cake family. this could also explain why she stays at cake's house, obviously as well as working for them, maybe just miss cake knowing all this intertwining decided to hire her and host her.