Perona was a popular contender for NN because she matched well with Nami and Robin in the "Three Faces of Eve" trio dynamic. Nami and Robin both fit well with the seductress and wife archetype, respectively, leaving the child spot empty. Perona or Shirahoshi could have worked well, but they kinda blew their chances (not that they even had one in the first place).
We also have the "Hecate Sisters" trio dynamic. Nami and Robin both work as a seductive maiden and a eccentric mother, respectively, leaving the sarcastic crone out. Note that the crew doesn't have a "Grandmother" figure yet.
So, if we do get a third female in the crew, odds are that she will be either an innocent and/or immature young girl or a sarcastic granny.
The 2 dynamic relationship within the female characters you proposed was insightful. Definitely a strong possible characteristic for the third female nakama, if it will be a she. And between the two (immature young girl or sarcastic granny) I would think that the latter would be the better option as we really don't have that personality in SH. And granny is really the lacking figure within the dynamic group. We have the nuclear family covered. Grandpa within Brook and relative w/i Jinbei. Jinbei I suppose could play the sarcastic card as we really don't have much of a clue as to his personal character sans his chauvinism and honor.
Although, I'd be pretty disappointed if the char design were to look like Kureha or Tsuru. I'm loving me some cool and energetic looking member. Brook works as an SH member and grandpa figure because he is a freaking skeleton with lame bone jokes. If it were to follow the hecate sister trend and the option were the chars introduced before New World, Bonney would be a good fit. Due to her being able to change her appearance, it really obscures her actual age. Some proposed that she is really young, and other say otherwise. I think judging from her action with the drama covering Zoro's recklessness with the Tenryuubitto, she IMO is an older lady. Her personality could be developed into the sarcastic type, as of now we don't know what her personality is. Heck, she could even be the young type and the dynamic within the female chars would then be the three face of eve too.
It'll also be interesting as Luffy will have eating competition with her. Sanji will have to constantly cook for her while constantly trying to impress with his food. Zoro x Bonney I could already see. Brook and Bonney (if she really was way older) sharing wise thoughts, telling experiences, having respect for each other while, time to time, nagging to see her panties. Ussop,time to time, would be outlied. and Chopper would sometimes have a buddy of the same age, or a Nanny that will tell tales of wisdom. Everyone would be absolutely charmed or annoyed by her sarcasm. As far as SH role goes, she might be the spy/scout type because of her ability to change her appearance. This ability was what I wanted out of Bon Clay (we now know he's not joining us).
On the flipside, I don't know the upside for her ability. Obviously against boss-like crew she can't just down/up-age her opponents cause it'll be too deus-ex-machina. Plus, as of current, there really isn't anything that will make her leave her crew. Also, we have yet to know if she has a dream to fulfill or not. And it also seemed she has too much alpha dog quality to be with Nami or Luffy. And she isn't a Logia, I'd really love to have a Logia in the crew. Like someone said, I think there isn't a clear advantage anymore possessing a Logia ability in the New World. Maybe this Logia ability would be picked out by someone in the crew already in the near future, so my point of Bonney not a Logia type would be moot. (I actually cringe at the thought of a non-df crew member getting a df power).
All in all, I'm not oppose for Bonney to be a part of SH as I can see her fitting quite well with the dynamic of the group.