Hi there, There sure is. Just go to the ideabook and click the collaborate button near the top of the ideabook. You can add collaborators on both public and private ideabooks. Private ideabooks will remain private, visible only to you and those people you added to them.

Thank you! I think the problem was the person I was trying to share & allow to edit was not yet a Houzz user. She just signed up since I sent my question, & now I get the option of letting her edit the private board, using your directions.
Thanks much.
best,
Fannie