There is some anecdotal evidence that it can be helpful as a neuroprotective agent, but I would expect most of the effects to be palliative.

Truly, with a diagnosis like ALS it is about whatever gives the person the greatest amount of comfort. So if being high all day is a happy place for them, I'd say go for it. It will help with some of the common side effects no doubt (pain, spasm, etc) but there will be an upper limit on the utility.

As for solid evidence? None exists that suggest it will certainly lengthen lifespan, but what anecdotal evidence there is suggests a pretty rapid onset of relief with regular dosing--so your friend would know in a weeks time or so, ostensibly, if it was working well for them.

It helps relief of symptoms like pain , tremors and encourages hunger and helps with sleep comfort but it does little to stave off the disease itself in small to moderate doses.
Best of luck.
Peace