How did Talia find her father?

ahem

There's these things called telephones. In the era before cheap, pay-as-you-go cells (aka 'burners'), you were restricted to landlines. To set up clandestine calls, have someone call a payphone. In the advent that you want a more 'permanent' solution, have a 'retired' member maintain a phoneline, have people call them, and then the lieutenant calls whatever number you've last set up for them, passing on the message.

Here's how I see the last conversation between Ra's and Talia's mother going:

"Ra's, Daddy's at the door!"  
"Oh dear - I'll try to escape, but we should meet up afterwards"
"But how will I find you?  You'll have to leave the country!"
"Here, take this phone number.  Tell the person on the other end where you are."
"Goodbye, take care!"

Obviously, her mother never got to make that phone call (or some variation on passing messages this way), but she could have told Talia how to find her father.

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