They just gave us her in hologram-form, her voice, her tombstone, her picture, her dog-tags, and references via dialogue, and it was their way of ushering her out in as clean and as graceful of a manner as possible.
She's gonna show up in Covenant 2!?? No chance. People by then would REALLY go "who the f**k is this?" If anything, give us more slices of Guy Pearce. That would at least make sense.