Dalby red is broadly fine for a novice, it’s harder on brake pads than your skill set in honesty and the tougher bits can easily be walked.
There is/was one small bit which was badly worn towards the end (assuming you parked at the visitors’ centre) maybe 2/3rds of the way last time I was there that I wouldn’t be comfortable leading a novice down as the line choice wasn’t great and typically one of the more awkward bits to walk round – down would be fine if it’s not too busy. (oblivion maybe?) Essentially you entered a worn berm/switchback which dumped out into a worn rocky section with a couple of small drops and the slower line was badly cut up. It may well have been repaired by now though.
I’d be comfortable taking my Mrs round the rest and have done most of it with her.
It is however a reasonable length for someone who isn’t used to riding a lot.