I am in the same boat as your wife brother. I was on Paxil for 5 years. At the time I was put on it, I definitely needed it as I was suffering from major league anxiety/depression. I was never told at that time how much weight(fat) that SSRIs can cause a person to gain, and thus never adjusted my diet or anything. I believe that I was actually told that it would make me lose weight of all things. Nothing could've been further from the truth. Being that the Docs didn't inform me properly, it took literally YEARS, and eventually finding these Boards, for me to understand that the Paxil was indeed the reason I was gaining so much bodyfat. Initially, I thought that I was getting old, or sedentary, or whatever. Problem is though, is that noone in my family works out exept myself, we all have desk jobs, yet I was the only one who couldn't eat whatever he wanted w/o gaining MASSIVE amounts of fat! I think that initially, I put on 40 pounds of fat(went from 190 to 230) in like 6 weeks, I shit you not! Eventually, I adjusted my diet, and took alot of the weight off. The problem was, was that the diet was so low in calories, that it made me more miserable than eating my fill, even though I was shedding pounds. I mean, we are talking bunny rabbit meals here. VERY small.
I feel for your wife. The reason I went off them was because I decided that at this point in my life, I would more readily accept being psycho and skinny, than layed back & fat. Being a skinny psycho is WAY more socially acceptable quite frankly. I went off of them about 5 months agao. Initially, you feel wired. Luckily for me though, it was an easy adjustment. I am fine now, and didn't go back to the previous mindset I was in 5 years ago, when I was initially prescribed the drug. I can eat now too.
As far as recommending something for your wife, I can't and I'm sorry. Does she have an outlet for her tension/anxiety/depression? Does she workout? If not, maybe you could get her into it. Something to occupy her thoughts & time perhaps. Of course, St. Johns Wort is said to have positive effects, but who knows. I couldn't say for sure, as I have never tried it personally. It's worth a shot though. It's right down the street at Rite-Aid if you want her to give it a try. I wish both of you luck bro.