The more you think about it, the more Sakaki working at Flower Jambo seems to make sense. Sakaki is very knowledgeable about flowers and wants to do this for a living anyway. She loves little cute things, and what's littler and cuter than Yotsuba-chan?
But on top of all that - Despite how big she is, the presence Jumbo and Jumbo's dad will always make her feel tiny.