Maybe they're saving her for later like you said. I don't mind her not appearing immediately but I hope they aren't replacing her with Dazzler, particularly in terms of a group dynamic that has nothing to do with Dazzler in the comics.
Jubilee, like Kitty, kept getting endlessly recast. Kitty lucked out with a bigger role in X3 whereas Jubilee remains in the background. I feel bad for Jubilee though because I don't think any other character has been as unlucky as her in terms of X-Men movies.
She was the original choice for the Rogue role in the first X-Men movie. Apparently, movie execs learning she was actually Asian and not white is why she got replaced last minute. In X2, her main scene was deleted. In X3, she's barely visible. In DOFP, she was supposed to be part of the future team (I think played by Jamie Chung), but she got removed. And then in Apocalypse, she never had a huge role despite promotion pretending she did, but 90% of her few scenes were scrapped leaving her with I think only a minute of screentime.