Is there a source for a woman not to leave her home after birth without hearing kaddish in a minyan?
The Sefer “Bris Avos” mentions this custom, though it is not prevalent and doesn’t seem to have a clear rationale.
I saw suggested that there might have been a custom for a minyan to be present at the mother’s home, in order to allow her to make the HaGomel blessing. Over time, the purpose of having the minyan in her home was forgotten, and what remained of the custom was that a woman must remain at home until she hears Kaddish from the minyan.
At any rate, as noted the custom is not prevalent, and there is no need to be particular for it.