Ike & Jack,
I found statement made by Mrs. Box that had been transcribed from NARA files. The reference was at the littlebighorn.info under Satana, Kiowa chief. I copied it and will send a PDF to your emails. It is rather long to post here.
The Richard sisters are written about in the book "The Great Sioux Nation" by Frederic Malon Hans.
The Richard family moved to the prairie to ranch. The mother stayed in St Paul with plans to join them in two months. Bertha age 17 & Mary Richard age 21 were taken from their family's ranch cabin on Heart River on Dakota prairie (about 75 miles west of Ft Lincoln) after death of her father F.D. Richard & 3 brothers Jerry, Mark, & William at hands of 7 Sioux warriors. They had been preparing a meal to share with the Sioux. This was July 14,1876.
The mother came out three weeks later and discovered the bodies of the dead. Troops from Ft Lincoln buried them.
The author Mr. Hans was a hand at finding & recovering women captives. He recovered 17 that had been taken from border settlements. He had been part of treaty negotiations and was known to many chiefs. He traveled from Indian camp to camp with lists of names & photographs of white captives in his pocket.
He found a girl whose photo he had--Bertha in Spotted Elk's camp July 30, 1877 on Powder River, specifically as one of his 4 wives. He had paid value in gold $200 of 12 ponies. The previous purchase price from Red Bird a month earlier. Spotted Elk was very reluctant to part with Bertha. So Mans threatened him with Miles who was developing Ft Keogh 60 miles away and Ft Custer troops 100 miles away. Told the chief his entire group would be wiped out so best to take the gold in exchange for the girl and information on location of her sister.
Bertha insisted on traveling to White Cloud's camp to find her sister Mary. It was at Beaver Creek but had moved to the Little Missouri by the time they arrived. He negotiated for Mary with White Cloud who was subordinate chief to Spotted Elk by telling him the more senior chief had told him where to find him. Plus threatened him with the cavalry troops also. He gave 8 ponies for Mary.
He traded with his friend Brave Wolf for 9 ponies with promise of $150 gold after he returned to Ft Lincoln. Mary rode one of the ponies & both girls were returned to Ft Lincoln to their mother the first week of August 1877. They were held more than a year.