I must admit I don't quite understand why the expectations of the any other players, or the DM, have anything to do with the way your wife wants to play her character. Surely she can play the PC the way she wants to play it, and it's the rest of the group that should bend to fit..? I have first hand experience of this problem when a player in my own group was on the verge of being persuaded that the only 'viable' option for her character was the party healer. She almost capitulated before I found out what was going on and put my foot down. Now the party doesn't have a healer, but she's playing the mad gnome she always wanted to, and it becomes my job, through whatever means, to make sure the game still works for them. That player was the least experienced player in the group and probably more vulnerable to pressure from the other gamers with more roleplaying levels under their belt. She also happened to be my wife.
It also seems to me that if your wife is having a stressful time outside of the game, then the game should be there for her to blow off steam, and that means she should play a PC that she enjoys, in a manner that she enjoys. Currently that seems to be as a straightforward righter-of-wrongs, with none of the intrigue or machinations that she has played in the past. This may be upsetting the expectations of others, and may also be derailing some of your DM's plans (which only exacerbates the earlier problems), but unless it completely and utterly throws the campaign off its stride, exerting pressure on her is just going to alienate her from the group. For myself, I often find that the kind of games I want to play and/or run are directly influenced by what's going on at work; the more stress I'm feeling, the bigger the escape needs to be, and that often means picking up a sword and hacking at my enemies rather than bringing them down from within.
Hope that was remotely helpful.