Nanobots' discretion

Could it be that as the nanobots are fully aware that there is already \r a Kochanski on board (albeit not the original)they simply didn't see\r the need to recreate another copy of her?Maybe they realised they'd caused \r enough trouble already. \r

Nanobots

I am fairly sure that the nanobots are programmed by Holly as part of his job to keep Lister sane. As such, Holly knew that Kochanski was with Lister and would have programmed the nanos to this effect.

Holly created his own set of nanobots and ordered them to recreate the crew. As Holly was in charge these nanobots recreated the entire crew except for Lister and Kochanski who already existed.

Rimmer destroyed Kochanski's disk

Okay, this is going to take a little explaining. Please bear with me. Let's be frank, how could the nanobots POSSIBLY take ashes of a human and rebuild their body with their personality and memories in tact? I'll be honest, I can't think of a way. However, Holly does have a neat little capability to resurrect people via hologram. Everybody's personality was stored on a disc somewhere on the ship. The nanobots could have taken that data and dropped it into the brains of the bodies they made for the people. Early in the series, Rimmer hid Kochanski's disk so Lister wouldn't bring her back on his run-time. If that disc was lost/destroyed, then the nanobots couldn't have brought her back.