This was likely done so that the franchise could cover its bases, just in case stars like Jennifer Lawrence decide to depart from their roles.
X-Men: Apocalypse introduced a ton of new characters to the franchise, giving us a glimpse into younger version of Cylops, Jean Grey, Storm, Nightcrawler, and yes Jubilee.
Adding these young newcomers will allow the X-Men story to continue, regardless of which classic characters return.
It shouldn’t come to much of a surprise that Lana Condor is ready to slip back into Jubilee’s yellow jacket.