Another suggestion is this, if any documentary evidence of the divorce proceeding during the time of the interview will solve the problem, then he should go ahead alone provided the court is ready to provide the documents needed, if not, they both need each other to succeed.
This is a real precarious situation and it must be handled with care and caution. I find it difficult to believe that a lady is adamant to follow thru with this process, knowing the benefit that awaits her with a green card. I dont want to believe that our friend has an axe to grind with the girl and that he is the one trying to exclude her from the program or that the guy is asking for real marriage before he will allow her to be a beneficiary.
Please, pardon my analysis above. I need to state my points before giving my advice so that you will appreciate my suggestions. If the above applies, then our friend has to shift ground and see himself and the lady as partners in a venture in which they both need each other to succeed, rather than seeing himself as a winner that wants to help a beneficiary. If he thinks like a winner, he may end up losing the opportunity.
I will advise both parties to sit down together and reach a compromise. They can go on their separate ways after the visas have been granted. If settled, they should proceed to snap as many shots as possible with several arrangee family members as possible. Their case does not elicit so much suspicion because the details of both parties were included in the lottery application.
If however the lady is still recalcitrant, our friend should approach the court for any documentary evidence that a divorce proceeding has been initiated. The process need not to have been concluded. The court will surely avail him something to show that the divorce process is on-going and that it takes so long to conclude.
It is easier and safer to remove a spouse than adding one after winning.
But if I have my way, I will prefer both parties showing up together a husband and wife.
Best wishes.