When and where she was born has little bearing on the train information as to when and where she died.
Information on the train:http://trees.ancestry.com/tree/8073961/person/-1000965830/st...
It departed on August 9 from Wyoming, Nebraska Territory, a Missouri River port, 44 miles south of Omaha. Listed were 375 departing (also found as being 350) and 47 died. They arrived October 26 in Salt Lake.
One documentation is the John Theophilus Gerber's journal excerpts of the journey.http://trees.ancestry.com/tree/4363719/person/-1615857769/st...
(For non-Ancesty members, also at:http://www.ancientfaces.com/research/story/404744
Aug 12, a little child died. August 13, a sister (probably means a female group member versus a family member) died, she was buried Aug 14, along with her son and two other children. Aug 16, buried another brother. Aug 17, another person died... this continues through the excerpts. This author may not have known the names of the victims, and only addressed them as "sister's."
I see you also posted on the Utah unknown board with more information:http://boards.ancestry.com/localities.northam.usa.states.uta...
You identified "Her date of death is very precise..." but, you didn't identify any date, or the source of that date.
I doubt there will be any record of her in Wyoming for many reasons. It appears from the journal above burial occured as persons died, not necessarily waiting to come to an occupied area. This corresponds with burials of passengers on other westward trains. On some routes, the trail was "covered with crosses."
The best potential probably lies in the Salt Lake Mormon library. I'd contact the library to see what additional information may have been in the above journal versus excerpts. Also, what additional journals may have been written and kept. The wagon master may have kept a journal, as he was ultimately responsible for the train and perhaps listed name and dates of deaths and burial.
While being "an old Ranger" myself, the National Park Service does have a Mormon Pioneer National Historic Trail:http://www.nps.gov/mopi/index.htm
I'd suggest contact, but they may not have the documentation you desire.