this is a common problem that is encountered with log shipping and mirroring when the servers are using disparate drives\paths.

Best way is to

• disable the LSbackup job
• run the LSCopy and then the LS restore jobs to ensure all remaining logs have been applied
• create the new file on primary
• take a manual differential backup on the primary
• restore the differential to the secondary with NORECOVERY and the MOVE option specifying the correct drive\path for the new database file
• enable the LSCopy job