Mom returned to the U.S. from Bolivia before her parents did. Here's a newspaper article and passenger list for the ship Leme I found on ancestry.com. Mom returned to L.A. 18 Jan 1927.
A 6,000 mile journey is pretty long for a 6-year-old. But then she got to stay with her maternal grandparents in Los Angeles, and I expect she was completely happy with them.
She said that after her arrival, her parents received a telegram saying "Miriam arrived ok. Dead." That shoulda been Miriam arrived ok. Dad.