Ok, regarding sneaking meat to your kid behind your back: get to family therapy NOW, and put your foot down and INSIST he WILL go. Use any leverage you think will work. The reason why: I am reading between the lines here and I think he may be trying to "get you back" for something (maybe get you back for going Vegan, for changing??). Going behind your back for anything points to a very bad disconnect in the relationship and very unhealthy practices that will almost certainly get worse. The action is passive-aggressive and undermining and I find it extremely disturbing on many levels. Even if you were divorced, this would be a bad thing for him to do.
Now, about that - I am going to give you a dose of reality here... When you made the child together, you both were in a different place, and at that time you both had a different commitment to how you were eating (and presumably how you would feed the kid). You both have now gotten away from that original plan. He has gone to a less healthy but more flexible paradigm, you have gone to a healthier but more restrictive paradigm. There is no way this was not going to cause a conflict and someone is going to have to compromise somewhere.
How old is the little girl? Is she old enough to make anything like an intelligent choice on what and how she eats? If not, then you are all now stuck with a nasty choice: either you, the parents, find one plan you can agree on for the child or you each feed her the way you like which may be tough to do If you stay married - it could lead to more conflict which would be bad for the child. If you split, it might be easier, if you can find a way to do it peaceably. Ultimately you both need to do what is best for the child.
Note: while I do think a Vegan diet is healthier for the child, you very well may not be able to convince your DH of that. (You definitely will not convince a divorce court.) Thus, you may not be able to achieve your desire of raising your daughter Vegan. if you decide to stay with DH, then I'm betting you will have to compromise, at least for the forseeable future.