how many KB in size is the transaction?
check the command line options as they are different than console options...in windows I start qt from command prompt like this: litecoin-qt.exe ---help
in linux its ./litecoi-qt --help
should be close in mac...just get that help screen from command prompt
there is a command -assumevalid=hex
you may need to lower your mempool requirements...if the transaciton is under 5kb in size then that is why its not confirming...
Keep the transaction memory pool below megabytes (default: 5)
have you tried reindexing already?
here's one option I do NOT recommend...but it may help if that transaction is the only one...Do Not Do tThis if you want to keep the transaction
Delete all wallet transactions and only recover those parts of the blockchain through -rescan on startup (1 = keep tx meta data e.g. account owner and payment request information, 2 = drop tx meta data)
maybe it will up the fee so it can be mined into a block...