How can my daughter file for divorce while in prison?

It can be done no problem. Use of a lawyer is recommended.

She can obtain the necessary forms from the Court, on-line, complete them and give them to you for filing. Next, you can take the Petition to the local Sheriff to have it served on her spouse. That will begin the process. From there, it will depend upon whether or not her spouse will agree to a default divorce or whether or not he will oppose it.

What she needs to do is get an attorney and file for divorce. Perhaps it can be an uncontested divorce which is relatively quick and easy if the parties can agree upon all of the issues.

Usually she must file in the state where the marriage was last intact (parties lived together as man and wife). Here probably Rhode Island. No special procedure is used because a party is an inmate.

You don't indicate whether they have any children together or own any property together (house, cars, bank accounts, etc.) that needs to be divided, but if not, then it would be a rather simple process if her husband wants the divorce too and she knows where he is. If not, then it can still be done, but may be more complicated and require more time to accomplish. If she has access to a computer, the internet and a printer, she can download the simple dissolution of marriage forms from the FL Supreme Court website, or someone can do it for her and send them to her. If they have children or have property to divide, she should use an attorney to assist her.