I find this a lame excuse. For all the other characters two and a half years have also past and they obviously have no problems to write for them. I think they could have made her fit in the movie, if they really wanted.
You mean a movie where there are the original seven, Jaylah, Krall, the Swarm, Starbase Yorktown, the Franklin? There's a lot of ground to cover. I'd rather she not be there than just be a token presence so some fans don't get sad.