Just thought of something. More a relationship advice that might help in the long run here. If you want to avoid lawyers, this is just about the only avenue you might have. First, you need to do your research and ensure that you know the whole (lawyerless) divorce process from beginning to end. Who you have to see, what you have to fill out, how much you have to pay, how long you have to wait between each step etc.... Then onto the hard part.
Communicating with her seems to be unpleasant, but I can't imagine that it is all from her side. You have to be doing something that gets her heckles up, I am even sure you know what it is (tone, wording, attitude, etc...), but just dont care to turn it off because you dislike each other. WELL, turn it off right now. Not to try to save your marriage, but to have a chance at speaking openly about this with her.
You need to have as calm a conversation with her as possible, and then ask her if she is unhappy. Put her feelings before your own for just a minute and get her buy in. Slip in the word divorce if it feels right and try to calm her as much as possible. Do the opposite of what you normally do when she blows up. Talk her down and put the focus on your mutual happiness.
Use whatever conversation points you might have.
The reason I would say that this might be an option is because blindsiding her with a pre-organised lawyers letter, can be interpreted as "going behind her back", as twisted as that logic might sound. A woman like this is 100% guaranteed to get vindictive if you hit her with a Lawyers letter or divorce papers straight of the bat.
But if you make it a conversation, and simply show that you have done your research on how best to do this to make it as quick and painless as possible, while tapping into whatever good feelings you two must have shared to get married in the first place, then you might have a chance at keeping her amicable. Print off whatever research you can. Give her the same information that you have, so that she can assess it herself. If you dont do that, she may take the short cut and go to a lawyer for advice. Then the lawyer traps her in and tries to screw you.
Tread carefully if she has crazy friends or a crazy mother. Either of those will chuck a spanner in the works.