It's far easier to raise a family if everyone sticks to the same dietary decisions. Our rule with the kids was "if they are old enough to know what they're eating, it's their decision". The eldest tried meat a few times, the middle one nibbled at it a couple of times, and the youngest hasn't so much as licked it. All three are what I consider lifelong vegetarians (16, 18, 20 now). Breastfeeding is obviously dairy, but once they move to solid foods it takes a LOT of knowledge to raise them vegan and not neglect something they need to grow. It clearly isn't impossible, just difficult.
In contrast, my wife and I went vegetarian before our first was conceived while two brothers (and 30+ year friends of mine) married carnivorous women and while they have both maintained their vegetarianism, both of their wives like the convenience of McFood and their kids have suffered the health effects from eating such things. That's been a major point of contention in both of their marriages.
Frankly, I think she'll be pleased by your decision. I'm sure she has had concerns about the impact meat could have on you in the long run. Vegetarians and vegans tend to get along quite well, but you've probably already dealt with that issue. The harder thing for me was dealing with my parents - "Chicken broth isn't vegetarian?" When I met my wife in '84 I was still a heavy chain smoker. I quit about three months later, and yes, it was partially because of her. But it was also because I couldn't breathe!
Hang in there and just keep a positive attitude about it.