Need input quick!

My son is a military man, has been for near 15 years now.  As long as he has been active duty, it seems that he is deployed for at least 6 months out of the year.  About 7 years ago he met a nice gal who lived in the city where he was stationed, things progressed and they married.  She was fully aware, of course, that he is active duty and what was required of his service.  6 years ago they had my grandson AND, were informed that they would be stationed elsewhere. 

DIL had never left her hometown, and their destination was to a rather small city, in the middle of New Mexico.  She is from a beach resort city in Florida.  Ever since they have been there, 4 years now, she goes nuts when he deploys, crying, pitching tantrums, breaking things and then mopes around not really doing more than going to work and feeding my grandson.  She constantly complains to her parents who are under the impression that she lives in a hell hole with no running water or plumbing. 

What this does is create a lot of un-due stress on my son who worries about her and his son when he is overseas and should be simply concentrating on his job and staying safe. 

I have offered time and time again to go live with her when he's gone, to bring them to my place (4 hours away) while he's gone, or anything to keep her spirits up, but she flat out refuses and says she's tougher than I give her credit for.

This week, my son came home from 3 months overseas.  He called me when he got home and was crying.  My son was crying!  He said that my DIL DESTROYED all of his guitars (he had 5!), all of his paintings and art (he's a darn good artist), that his car was "wrecked", and their back yard was destroyed; all their lawn furniture slashed and broken.  To top it off, DIL simply told him she had "reached her breaking point" and for him not to worry because she'd replace it.

I don't know how to help!   I know they need couples therapy, and that had started, but now he says "he's done".  He said that he called the MPs and made a report and she called her parents, who were "shocked" that he'd get her in trouble like that...  

I'm headed up to pick up my grandson, my son asked me to come and take him for the rest of the week so he can sort out things.  He's so down.  I hate to see him like this.  Its been hard enough over the years watching his spirit get stamped out from these ongoing wars... 

Sorry so long, I just need a shoulder and some real solid words of wisdom....  TIA

~Worried mom