On further examination, it does not see the file on the left side when in Library either.
By "file" it would seem that you mean "folder" or directory.
If the Folders panel is not showing you the desired folder, first check to see if that is solved by right-clicking the child folders and selecting "show parent".
If you have not imported any images from that folder, then LR will not show it to you since LR is not a file browser.
If you do have images imported from the folder, find one, right-click on it, select "show folder in Library". Also try "show folder in Explorer/Finder".