In livemesh grid widget you ll be able to create query in “Build post query” window there you can add the required category ..
Pls check this thread – https://siteorigin.com/thread/build-post-query-widget/ explains how you can add specific category in the taxonomy field.
If still you find any difficulty you can add text widget instead of livemesh grid widget and insert show_post_snippets shortcode with taxonomy and terms specified .
[show_post_snippets post_type="gallery_item" taxonomy="gallery_category" terms="international publishers" number_of_columns=1 post_count=1 image_size='medium' display_title="false" show_meta="false" display_summary="false"]
The details of shortcode is available in theme documentation.