If a JW admits to a disfellowshipping offense (and adulter qualifies), there is no need for proof. A confession is proof. What happens next depends on several factors.
If she says she is sincerely sorry and promises never to do it again, if she weeps and the elders think the tears are genuine, if she happens to get a committee of brothers who are sympathetic to her and not hard liners; IF all of those things happen, she may be privately reprooved.
You haven't supplied very much information. For instantance, you said she is in the process of obtaining a divorce.
Is she still living with her husband under the same roof?
Is she still attending meetings?
Are you the other party to the adultery?
Do you intend to marry her?
Is her husband in good standing in the congregation and do the elders know/believe the abuse?
Does she want to remain a JW?
If you answer these questions, we may be able to answer yours.
Wasa
PS to Simon: what is up with the formatting of the above post?