There are a group of men and women riding across the wild west, there is a stagecoach, the indians catch them and one of the women hides her jewels/diamonds in her mouth to hide them from the indians. She plays dead. One Indian realises this and makes her swallow her jewels and she subsequently dies.

Shalako (1968) (http://www.imdb.com/title/tt0063592/)

Great, many thanks for your help.