That site has useful information. I thought you could use it as a start. It seems to be pretty easy to navigate with everything very compartmentalized. I just googled "benefits of breastfeeding for mother and baby."
If you can get her to attend a meeting with the other women there in TPE, that may help a LOT! I already knew about all the benefits to both mother and baby, and I was still ready to quite at the three month mark. I hadn't gotten that far when I got mastitis. It was very, VERY painful. I insisted my ex go out at 11 pm one night and buy our fist can of formula so that I wouldn't be faced with another excruciating feeding, but he talked me into trying just one more time--promising on pain of death that he'd go straight out after the next time I nursed if I told him to, no more questions. But the next time went wonderfully!
When your baby is still small, nursing--which should seem the most natural thing in the world--can be very difficult. You have to sit there with either not enough milk (my son sucked blood from me for the first three days), or drenched in excess milk which seems to pour from one breast faster than you can absorb it, as you baby nurses from the other. And that's if the baby is latched on correctly. Usually, you're breasts are heavy, warm, and covered with tiny hickies! Depending on delivery methods, it's also sometimes just plain painful/uncomfortable to sit and hold your baby while it nurses. C shaped nursing pillows are available. Buy one of these for your wife if she doesn't have one. They really, really help.
And nursing will wear you out! I put up with a lot of nonsense because I'd be tired after nursing, but a woman's body is making milk, using its own resources to make it, and using its own resources to manufacture it. It takes a lot out of you! So bring your wife a glass of water--you get very thirsty when you nurse--and be extra sweet to her. She deserves it! You may think that the hard part is over because the baby's birth is over, but that's just the most painful part. You wife is still very constantly attached to this little one who needs her, demands physical strength from her, emotional stamina, and further sacrifice of her body itself. It can be very overwhelming and very exhausting.
Take her to a meeting. Talking to other moms about these things will help. Really.
P.S. I ended up nursing not for three months, but for three years! Most women will not do that, and that's okay. The point is that I got through the rough patch. You can help your wife through it, too!