It strikes me as an anachronism. I think she would address her father as "Father" or "Papa" for the time period. "Dad" seems too modern.
This positively infantile preoccupation with bosoms!Terry-Thomas about US 1963.Hasnt changed much!
She can call him Father, she can call him Owen, she can call him a Dirty son of a #@$% But calling him Dad, or Daddy is out!
"Dad" goes back centuries. Do some research.
shareMerriam-Webster says the first known use of "dad" was in 1533, though it doesn't say how popular it was compared to "father" and "Papa" in 19th century USA.
https://www.merriam-webster.com/dictionary/dad
This source says that "Dad" goes back centuries and is probably based on "dada" baby talk:
http://www.todayifoundout.com/index.php/2014/11/curious-origins-words-mom-dad/