Is there a way you can do this without using iframes? Maybe you can set App A as a dependency of App B and instantiate one of App A’s Forms inside App B.
It sounds like you’re using Data Tables as a way to pass data between two apps. Perhaps there’s another way to do that in this case. If you were using dependencies instead of iframes, you could call a method on each app that knows how to store the data in its Data Tables. If you can’t use dependencies, you could set up an HTTP endpoint that contains the code to store the data. In both of these approaches, the interface between App B and App A would always be the same, and each App A would own the knowledge of how its data is stored.