gc filed for spouse - divorce

[sejli]

one of my friends, a US citizen, has filed for a gc for her husband. the interview for this gc was in feb 02 and now they want to get a divorce. it is filed in vermont center. can somebody please tell me what is the next step and how long do they have to wait for his gc to come through so that they can file a divorce?
any help in this area will be appreciated.