I guess I can see where she's coming from, since they've not had Marlena go down that particular path over the years. But we've seen Kate and Adrienne both go through cancer, and now Paulina. Many have had brain tumors. Caroline had Alzheimer's, then when the writers kind of wrote the character into a dying corner, they instead changed it to the fictional Toppits Disease, which had a cure. Maggie has Myasthenia Gravis and was also unable to walk in the beginning. Julie had a heart transplant and a pacemaker. Stefano had diabetes, as did Noel Curtis. Theo is autistic.
All this to say, I don't see where a "Marlena has XYZ disease" storyline brings anything to the table, other than to have her shuffle around with an illness, while John moans and groans at her bedside, until she nearly dies, then rallies at the last minute and said condition is never mentioned again.