Mmmm, have to say, while I did understand his feeling, I would also look at it on the other side as well.
As a shop manager, she has good communication skill and certainly knows how to deal with others. Proof is she is being polite and very caring with customer and dealers. BUT that's because they are her customer, not her lit' brother, someone she knows she can trust, someone she knows she can shows her bad sides. And she has great respects for him too.
At least they are working together again, so all good.
Before I forget again, thank for the new chapter.