I'm just more concerned for her depressive states
Maybe her mental illness is not caused by the religion. Maybe she is medicating the mental illness with the religion. If she has depression, that's a mental illness and I think it always requires a doctor's analysis. Maybe there's a physical problem underlaying it. Some people have unresolved issues of abuse or unfinished grief and they just need help accepting it and working through it.
I'm not much for laymen diagnosis and treatment of illnesses. Maybe you are a psychiatrist but I'd think you're not since you are posting the problem on a public forum looking for suggestions. I think your motives are great. I'd just absolutely not confront her about religion at all. If she is searching for information, I'd just answer questions that I objectively can.
As far as the Watch Tower goes, I'm absolutely convinced we don't get people to quit their religion by exposing them to the group's errors and I think untrained spouses make bad doctors.
There is a tremendous amount of evidence that much of what I say today will be my error of tomorrow. Best wishes!