I'm Doug, and I'm very sorry to hear of your daughter's situation. My goal is to provide you with excellent service today.
If more than a year has passed since your daughter was incarcerated, and she was sentenced before July 2014, then it will be all but impossible to have her sentence modified---because that would require the consent of the Prosecutor and that is highly unlikely to happen.
However, if she was sentenced after July 2014, then she will not need the consent of the prosecutor and she may apply right now for a modification of her sentence.
So, in direct answer to your question, there is no minimum time which must pass before an inmate can seek a modification of their sentence under Indiana law. Here is a legal link that you may find informative: http://www.awmlaw.com/HOW-TO-OBTAIN-A-SENTENCE-MODIFICATION-IN-INDIANA.shtml
You may reply back to me using the Reply link and I will be happy to continue to assist you until I am able to address your concerns, to your satisfaction.
Please know that I answer your questions in good faith, providing you with the information that you ask for, and I do that with the expectation that you would act likewise, and rate my service to you. Rating me costs you nothing as you have already paid the deposit for my help. All rating does is ensure that I am paid for my time in working with you. So, please do be sure to rate my service to you. Rating is accomplished by clicking on the rating-stars on your page. Thank you in advance for your positive rating.
I wish you and yours the best in 2016,