I suggest that knowing he was kidnapped by pirates supplies 1] a more substantive inciting incident than “goes missing”; 2] a more specific objective goal; and 3] telegraphs the promise of more serious jeopardy and high adventure: she must not merely find him, she must rescue him from slavery (the usual fate of human booty in the pirate economy.)

When her sailor father is kidnapped by pirates, his headstrong daughter disguises herself as a boy and joins a Phoenician trading galley to find and rescue him.

(One plus factor of the premise is its historical malleability: that is, the situation would work just as effectively in any time era until the early decades of 19th Century when pirates were finally eradicated from the waters of the Mediterranean Sea.)