I'm "convinced" a former boss character is to be their partner, prior to the new world… Which means, a limited number of so and so's could fit that role.
Granted the validity of the quote, she's one of the few to accept that role.
I'm more so convinced that there will be "two" more Strawhats to come, disappointed a little that it won't be characters that "share" the similar time frame of the journey, like the current cast, but that's nothing.
Given that the "chances" a female character will join seem half and half, I'd think it's more likely a lady would be it.
Considering that Perona has enough space to write anything about, and a solid character build that lets Oda use her enough to establish such events... She's the most flexible in terms of "strawhat-esque" story development.
Aside from all the other characters in the manga, she's the ONLY character that stands a chance, up to this point, concerning a revealed character. Jinbei honestly isn't likely to join-- he's not likely at all.
Ten days since she's been on the island– ten days for her to disappear from the island.
Less than ten days since Franky's been on the island-- around that time, he alone would disprove any person on the ship.
Ten days would explain the "needed" closure concerning the ship's treasure and Perona's personal belongings. She can "AP" her belongings now, as revealed by the parasol back in the 561 or so chapter cover. She now proves it as a fact... She has a Kumacy, the one from her past, with her, which could suggest she's packed her stuff from the Sunny and left.
Ten days would have given her the "finality" that she sought when her character woke up on Thriller Bark all to pack up the ship with her belongings. Ten days would be enough to conclude everything.
Then again, the "treasure" was never used for anything, the act itself was meaningless, and the character herself was wasteful. Which is it? Ten days of solitary retreat, or of favorable preparing for the journey ahead. Or neither, nor!
I'd hate to pick a "Robin" style approach, but it's probable.