Wait a second. Does Sunny actually OWN that smoothie kart or is she working for someone else? In the movie, it honestly just seemed like a one-off gig to sneak into CanderLogic. But, she's been keeping at in TYT. And we've never seen a boss. I guess it makes the most sense just to assume she owns it.
But, I don't know. It's never seemed like she has a real "passion" for smoothies. She's not constantly trying out new recipes or creating new smoothies and naming them after her friends. It seems like it's just a "job" not a "career". Mind you, keeping the peace between the different tribes might be a full time job enough, but still.
She actually seems to be an employee. Her full size cart in MYM does appear in A New Generation, but someone else is working in it. Maybe Sunny's gotten a promotion since then.
Hasbro seems to think she has a passion for smoothies. Her delivery cart has appeared in merchandise a couple times already. Maybe it's just because they know she looks so darn cute with her little helmet. And earth ponies have been strongly associated with food since G1.
Posey's rage is justified yet again.