Isabela Moner is rumored to be in running as the lead female character in Transformers 5 according to The Wrap. The 14 year old actress had performed on multiple Nick TV programs including "Dora and Friends: Into the City" and "100 Things To Do Before High School". The role is described as "Izabella, a street-smart tomboy who grew up an orphan and was raised in foster care. She counts a small Transformer as her only friend… until she meets Wahlberg’s heroic inventor Cade Yeager." There has been zero talk of Nicola Peltz returning as Cade's daughter. Without her character, it probably seemed pointless to try to add the now very busy Jack Reynor (Shane) into the film.
Considering Bay likes to sex things up with the ladies in his films, the potential underage casting is a bit strange but maybe its a directive from Hasbro whose Transformers toy line does not do well with girls and has been dropping in sales volume for the last few years among teens and pre-teens. As is typical of Hollywood and high level corporate execs, the solution is just throw children into the film of the proper demographic. While it rarely works in reality, on paper its comes across as a good solution. I don't have a problem with the idea of a 14 year old being a major cast member of the film as long as the story treats her as her age. By that I mean doesn't treat her as 18 (yuck) or use youth/inexperience to kick off an overall pointless action beat or move plot to next story point because "kids are stupid" type thinking. Neither does shoehorning an underage character into an otherwise adult character work out well. Also bit surprised this rumor even exists considering child labor laws kick in which would strictly limit how much Bay could film with the actress each day. As always, nothing confirmed officially so usual grain of salt warnings.