Can you explain to boss's daughter that they are elderly and they may not want contact for all sorts of reasons unconnected and she really can't go crashing into their world. I would be blunt with her to be honest.

Explain that she should write a letter explaining who she is and enclose her contact details, address and phone numbers, perhaps even a SAE too, that you will post. I assume being elderly they may not have any form of computer or smart phone.