That's definitely on my to do list.

I haven't done it, but I coached people for the Death Ride for years and have also done quite a bit of hiking between 10 - 14,000 feet. I would look at the training in 2 parts:

1. Training for the climb. This part is easy - what Eden said. Hill repeats, focusing on steady climbs. It doesn't seem like its a particularly hard ride once you take elevation out of the equation.

2. Preparing for the elevation. It seems that half the ride is going to be over 5,000 feet, which is where some people start to notice effects of altitude. This is a completely personal thing - whether and to what extent altitude affects you. It would be critical, I think, to have your client spend several days riding at elevation to start to understand how it affects her.

Some of our people noticed real breathing problems and dizziness above 7500 feet. Some got nausea. Others had no effects at all. I don't think you know til you get there how it will affect you.

In my climbing (on foot) over 12,000 feet or so, I observed it also didn't make a lot of different whether someone was "fit" or not (to a point). It really seems that elevations effects are more targeted than that. A less obviously fit person may be little affected by elevation.

So my recommendation would be an exploratory training camp of sorts where she can do some rides that get to 7000 feet or so. I'm not sure if you have roads that can get her that high. We certainly do in the Sierras if she could make a road trip - and by the way most all our roads are open because there's no snow!! I'd say spend 3 days riding and really feeling how it affects her.

And acclimatization is largely not attainable by normal (employed people). Altitude actually has deleterious effects for at least the first week or so, so you're gradually losing fitness (largely through dehydration) for that period of time. After a couple of weeks, you can start building extra red blood cells, etc. But it really takes a long time before you start getting beneficial effects.

Also preparation for the change in climate is going to be critical. Hawaii is balmy, but I suspect that will be a cold descent toward the top. She should prepare herself for always unpredictable mountain weather!!