Well there's your answer, it's not part of the Xara assets export and publish list because your LR folder and all it's files are not part of the Xara document.
There's nothing you can do about this other than have you LR folder outside of the index_htm_files folder and rewrite the iframe link. You will have to upload the LR folder manually using Filezilla then you can upload the Xara site via the publishing feature.