Finding medical records for Richmond State Hospital patient?

There is not likely to be any specific information about your relative's diagnosis and treatment, merely admission and discharge dates. The hospital's website has a page about genealogy requests that says:

Unfortunately, we do not have the original medical records of every patient treated at Richmond State Hospital. Records keeping laws and practices have changed over the years since the hospital opened in 1890. Today’s retention policies require the hospital to store the complete medical records of patients for 10 years after their discharge. After the required 10 year retention period, a 5 percent sample of records is sent Indiana State Archives and the rest of the medical records are reduced to the summary documents of the hospitalization. The excess medical information is confidentially shredded. The hospital has reduced medical records of patients discharged starting in 1979. The medical records of all patients discharged before 1979 were destroyed, except for a 5 percent sample sent to Indiana State Archives. However, the hospital does have basic admission and discharge information from the register books for patients discharged between 1890 and 1979.

In case the medical information about your relative is still available, the website also says:

Descendants requesting copies of medical records for genealogy purposes may contact the Health Information Services department at phone number 765-935-9234 or mail a request to Richmond State Hospital Attention: Jay Wenning 498 NW 18th St, Richmond, IN 47374. You will be asked to complete an “Authorization for Release of Information” form, provide a copy of a state issued photo ID, provide proof of a familial relationship and provide a copy of a death certificate if available.

There is also a museum most don't know about that is in the Administration building at the state hospital that is open to the public. In the museum, there are books that contain patients names, diagnoses and even medications. There are also pictures. Maybe you can find some answers there.

The hospital's website says:

During the hospital's 100 year celebration in 1990 we established our own museum bringing artifacts, antiques and records together of our rich history. The museum is still in existence today and is located in one of the wings connected to the Administration building. The location of the museum provides participants to view how life was like for our patients and staff in one of our original structures. Group tours of the museum are available by contacting our Community Relations Department ...

According to the Indiana State Family and Social Services Administration website, many of the early patient records were destroyed. Their site says:

There are some archive books listing very limited patient information. To contact Richmond State Hospital for genealogy records contact Jay Wenning the director of our medical records department.

That page also says:

Indiana State Archives (http://www.in.gov/icpr/archives/featured/csh_aiin/csh_hosp.html) apparently has some materials. According to their website:

    "Richmond State Hospital (1890-present) (formerly Eastern Hospital
for the Insane) Richmond State Hospital has served people with mental
illness from 18 counties in eastern Indiana for 105 years. Collection
Description: Annual Reports; List of Patients, 1887-1923; Medical
Records (sampling), NEED DATES. " 

Contact the State Archives for arrangements to search their collection.

On another page reviewing state institutions, the Indiana Archives and Records Administration says:

Richmond State Hospital (1890-present - formerly Eastern Hospital for the Insane)

This hospital, popularly known as “Easthaven,” opened in 1890 on a 1000 acre campus near Richmond in Wayne County. It serves counties in east central Indiana. Richmond is still in operation. As of June 2008 it had admitted 42251 patients. The hospital maintains a complete admission index. A sample of the medical records has been sent to the State Archives; the remaining records were destroyed.

You may not be able to get any information apart from the dates when she was admitted.

Before making a request for medical records from an institution or from the state archives, it helps greatly to organize everything you already have collected about a person. See Beth Foulk's post Creating Timelines to Make Sense of Genealogy Records from her site Genealogy Decoded -- she has also shared her Excel template which you can use as a guide. Timelines help us narrow the dates in which people might have been in the hospital, making any search in archives much easier to do.