John, son of President Coolidge had 2 daughters, by his first wife Victoria Moor; Cynthia who married a Jeter and Lydia who married a Sayles. You are correct, son Calvin died in his youth.
You can find the ancestry of Calvin Coolidges line at:
You would have to trace Louisa' lineage back quite far to determine if she somehow descended from an ancestor or relative of Calvin Galusha Coolidge b. 1815, as his 2 sons were John Calvin, father of the President, and Julius C who died at age 19.
What was Louisa's husband's name? Approximately when and where were they born and/or married? Was Coolidge her maiden or married name.
You should try the free search tool at Familysearch.org and see if you can find Louisa's (or her husbands) lineage. https://familysearch.org/