Wow....thats not answerable. I can tell what to do and not do once she has started a divorce, generally, but the things to do when she is thinking about it , ones that would make a difference anyway, are not doable....like eliminate the gaggle of friends that will say "whatever you want sweety we support you you know that"....thats just NOT helpful, and its ubiquitous.
I think begging is universally not a good idea, offering to do anything ANYTHING just please dont to this.....
Also, saying things like "even if you divorce me its OK I will always be there for you and you can have anything you want its your happiness that is the most important thing and I dont care about me"......bad idea, and not uncommon.
If my lawyer during my almost divorce, he with 30 years of family law representing men and women, had any wisdom, it was if possible, allow some negative to be present immediately for her at filing, meaning if she feels discomfort suddenly you dont look so much the jerk, because he said some huge % of the women he represented got really scared at the nearing of the final date, because they knew that the drama was over and they were unable to change anything else to "get" more or whatever