WS here, been diagnosed with Complex PTSD due to consistent and non-stop childhood trauma, neglect and abuse. C-PTSD is not something you can help your spouse with, other than being there for them, and being understanding of their condition. But healing from it is something they need to do on their own, and with a lot of therapy.
EMDR has been highly successful for a lot of people. I'm not sure why your spouse is opposed to it? There is nothing scary, weird or painful about it, at all.
When trauma happens in the brain, your brain needs to process that trauma. If that doesn't happen, then those feelings and the pain surrounding them get "stuck" in the brain (for lack of a better explanation). That's why people with C-PTSD can't seem to "let go" of triggers and often have extreme responses when triggered. When triggered, the brain processes the present as if it is still suffering in the past. It is like reliving a memory as if it is happening right now. (By the way, when I say a "stuck" memory, the person suffering is likely not aware of the memory itself, which only makes things more difficult to both diagnose and treat).
In order to release those stuck memories, it has been discovered that stimulating the left and right centers of the brain in fairly rapid succession causes the memories to "shake loose", at which point they can be dealt with. Stimulating the left and right parts of the brain is a very simple process. Each therapist does it a little differently, but the outcomes are the same. Some therapists will tap on your knees (left knee, right knee, left knee, right knee) while you do your CBT. Some may wave their finger back and forth, left and right. Others may use a little buzzer device in your palms. Again, none of this is painful or scary, and you are welcome to tap your own knees or do your own thing if that works better for you.
Sadly, your spouse currently has C-PTSD on top of an affair. Sometimes, BS's will find themselves feeling resentful about having to heal. It is simply the idea that, "This happened to me, I'm the victim here, so why do I need to do any work, shouldn't the WS be the one doing the work? This isn't fair." Unfortunately, both the BS and WS have trauma to overcome, and each has to do it for themselves. I would strongly encourage your spouse to learn a little bit about EMDR, or at the very least, speak with a therapist who specializes in trauma.
I wish you both good luck. EMDR isn't a cure-all, but it can really help sometimes, and cannot hurt, at all, so it is worth a try.