Bonney is a very interesting character, having a quite unique devil fruit and managing to enter the New World with a bounty over 100 million.
During the war she was viewing it from a distance, Whitebeard unfortunately died and she was seen crying and telling her crew that someone was responsible for this and that they would enter the New World and take them down. This right here sets her up to have a very interesting back story, she seems to have a past with Whitebeard or at the very least admire him immensely. With her age altering ability for all we know she could have been a close relative.[external_link_head] [external_link offset=1]
Bonney moves on into the New World and confronts Blackbeard, the man responsible for Whitebeards death. Her crew is wiped and she’s utterly defeated. Using her as a bargaining chip Blackbeard tries to trade her for a ship with the marines but the trade offer is denied seeing as they send Akainu, Blackbeards crew flees.
Akainu approaches Bonney and tells her “He was truly frightened when she escaped the World Government but is glad she’s back under their control”
This implies her fruit power, knowledge or heritage is threatening to the government or world. Maybe she’s a D? Maybe she was related to Roger somehow? maybe her power is more versatile than we’ve been shown? who knows, the point is she’s a big deal and in custody.
But she’s not. 2 years have past and she was clearly shown in the New World, only two possible scenarios would allow this. She escaped the World Government AGAIN, leaving Impel Down which is unlikely and a story that’s already been told. Or she’s working for them, still a part of the World Government. A Shichibuki, the seventh unrevealed Warlord of the sea. Offering to hunt down Blackbeard whom she already wanted to take down and is a big problem for the government, all the while keeping what ever makes her a threat to them in their control would surely be enough to allow her a pardon and the only explanation for her being free after being presumably taken by Akainu.
Moving on with the theory, Luffy has stated he wants to take down every emperor. Blackbeard is one of them. It’s safe to assume as he goes along this path more and more people will ally alongside him. Taking the rest of this theory into consideration Bonney will need to ally with the Strawhats to take down Blackbeard.
Her crew being wiped by him (by the looks of it) she may even join the crew after this, resolving her hatred for Blackbeard and avenging Whitebeard and what ever relation she had with him. Bonney would be a new female character with a unique design. Depending on what her fruit can do she may be a very strong asset.
Though her joining the crew is straying away from the parts of the theory that actually have evidence to back it up. Anyway wanted to share all this. Hope you enjoy the read, any feed back is welcome