There are many interesting fanfictions about a female Luffy. In some, a female Luffy might bring a different dynamic to the Straw Hat crew. For example, her interactions with male characters could have a new flavor. She might face different challenges based on gender stereotypes in the pirate world, which could add depth to the story.
Their relationship could develop through mutual respect. Luffy respects Whitebeard as a powerful and respected pirate, and Whitebeard respects Luffy's determination and potential. For example, they could start with a simple exchange of stories about their adventures at sea.
There could be an original character created just for the fanfiction. A woman with a kind heart but a tough exterior, who was a great fighter. She could have met Luffy's father during a battle and they fell in love, and she became Luffy's mother.
Luffy is still alive and kicking in the manga. The story keeps evolving with him at the center of the action, encountering new enemies and growing stronger.