Dennis,

The Union Catalog database is now available for online searching at

http://library.berkeley.edu/BANC/MTP/database/

I did a quick search for letters to anyone named Levy.  There are
only two listed.  One to a Helen F. Levy and one to Edwina L. Levy.
No Harriet.  Nothing in "incoming" from her either.

I'm sure there are an untold number of SLC letters out there still
to surface and be documented.

Barb