You can't do anything and neither can your brother. It is up to your neice to deal with her depression (very difficult when your get up and go has got up and gone but nonetheless still true). If she's had enough of counsellors and anti-depressants then she might want to look at a change in lifestyle, (diet and exercise can be of some benefit) but then that's also up to her to actually instigate and do. As far as I can tell, if she's unwilling to help herself at all then it would be up to the husband how long he can tolerate this attitude for and whether he's prepared to stick it out and hope the situation sorts itself out in someway. While this may seem harsh, depression is not something that other people can do anything to 'help' exactly, you just be supportive and sometimes you have to know when to cut your losses too.