Your Aunt is seriously depressed. While she may not have set to slowly kill herself, that is indeed what she’s doing. It is time she get in treatment, medical as well as psychological. What are the qualifications of the therapist? Does he/she know it’s not her house? It’s imperative the therapist knows the extent of her condition. Hoarding, not cleaning, IS a psychiatric disorder that goes along with depression and anxiety. If at all possible, one of you must tell this to the therapist. That she not in a wheelchair prior to her mother’s passing. It’s possible her husband is enabling her to continue in this downward spiral. If so, he needs counseling, also.
This is beyond a “We’ll talk it over,” kind of therapy. I think a visit to psychiatrist is very much in order. If she won’t go and her husband refuses, consider contacting your local mental health agency or report her (and husband) to Adult Protective Services. Unlike CPS, they cannot compel her by law or her husband to do anything they are unwilling to do. The only time that happens is if her home is in such disarray as to be hazardous to life and limb, ie. No plumbing, full of vermin, has urine and excrement lying about, is a fire hazard.
Yes, certainly pray, but action must go with the prayer.
You say she believes in Jesus. That’s a start, but hardly sufficient. The Devil believes in Jesus, too.
Can you find a priest who can reach out to her? Or can you bring one to her. She needs spiritual help, as well, to climb out of the pit into which she has dug herself. Six years is a long time.