Divorce is extremely stressful and with a new girlfriend involved, it can get pretty bad. I've been through it, so I can tell you that everyone deals with it differently and personally. It is like a death of a loved one, a death of something familiar and end. There aren't words to tell her to make her feel better but I found that talking to people in my same experience helped me.
Hopefully she has an attorney who is helpful, who can guide her means a lot. Having stable financial footing means a lot right now. She has to feel secure and she probably doesn't.
You're a good son to be as supportive as you are, so that's a huge deal. But she should look into finding divorce groups, talk to women who are also going through it, check online for her. If she's online, she should get educated on her divorce, make sure she gets all she is entitled to in her state. That fueled me for a while and believe it or not, helped because it made me feel as though I was in control, so all that anger was directed into my case.
Exercise, can't say enough about that. It does work miracles. Just walking put me in another mind set and physically helped me feel better.
I'd tell her to surround herself with friends who are going through the same thing even if it's only online.
I'm sure she has a hobby, have her focus more on that and deter her from drinking or taking anything to "calm your nerves". Mistake. Alcohol is a depressant and that's the last thing she needs.
Also...another great thing to do is to do something for someone else. Volunteer at a children's hospital or vet hospital. Sometimes giving outside, helps you on the inside.