The information you were given is only partially true, and the conclusion incorrect.
Under the new Story Group guidelines, at this time, the EU is not canon. This is obviously because the current films would not be possible if they held to the EU (which is almost all novel- and/or comic-based) content.
However, that does not mean that it all has disappeared and been banned. Simply that it is not canon that new media has to hold to.
They have also specifically said, and already begun, to mine the EU of the "best" ideas and characters and they have and will continue to do so. They just aren't beholden
to it, but they are free to pick and choose what to include in the new timeline. One example has been the new comics (which are canon) bringing in a former paramour of Han Solo pre-ANH from the EU.
It is widely speculated that the biggest reason they have gone out of their way to say that while it's not canon, that doesn't mean individual things can't be decided to be made
canon or worked back in if it's needed/wanted, is Mara Jade. There is even rampant speculation that she will appear somewhere in the new film trilogy.
In any case, I'm not sure of her chances of being part of DI are good or bad, it's difficult to tell where she ranks with so many available characters (though I do think she gets additional probability points simply from being female, as there are not a tremendous list of named females). If it makes you feel any better, in any case, DI has already proven to be the "exception" to a lot of mandates Lucasfilm has had post-Disney, including the downplaying of the prequels (which were obviously so played up with DI). Technically, there is already some EU stuff in DI (when it comes to origins/names of things that never were in films).
TL;DR? While I wouldn't guarantee that Mara will be made, any more than I would any other character at this point, if you like Star Wars - then you need to be playing this, it's really awesome.