Alright, so hear me out: What if the manager is on the side of wanting Yamada's happiness AND safety. I get barring her from going to school events is a "bad" thing, but that wasn't something they could control since it was the agency who decided that and they just have to do the things they are told.
I imagine there will be some sort of drama from this, but what if it turns into a big positive for the two instead of a negative. Her parents know and accept it without any issue. The real last hurdle is the agency/manager. Of course, don't really know where the manager actually stands outside of the extremely brief interactions we have seen, but that doesn't paint a complete picture of non-acceptance, just that there may be hurdles.
I guess we shall see how things go, but this manga always does surprise and delight me so I have faith things will work out.