Take psychology advice from a psychologist and insurance advice from an insurance professional.
I would talk to an insurance broker and explain your situation. Your partner can cite her specific circumstances and treatment timeline. Ask whether, in their experience, they think mortgage protection would be forthcoming.
If a doctor certified any updated diagnosis, then I doubt a mortgage protection company would challenge that. But they will still ask lots of questions about this aspect of her medical history.
If you find out that mortgage protection won't be provided, then you could consider taking out the loan solely in your own name and then trying to add your partner to the mortgage at a later point.
Keep your heads up. It feels stressful now, but you'll get there.