Would a desktop work? A high efficency power supply combined with an undervolted, possibly underclocked, (mobile?) CPU might be a viable option.
yes, a desktop would work - although her office space is small so smaller is better. But power consumption is the main issue.
One problem we have is that she is not entirely certain of the specs of her solar system, and unless we know that we have to err on the low side. We know she had no problems running a laptop, and in tests with a similar laptop here we know it draw around 36 watts. This is on an old Dell PII-300. I don't know how much variation there is between that and say a current model P4 laptop or a Pentium M. We tested a 19" LCD and that draws around the same - 30-35 watts.
She doesn't need the mobility of a laptop, but she wants a 17" screen, so the main reason for looking at a low power desktop is to save money. A 17" laptop is going to come in at around $1800. My thought is if we can work out a desktop system for no more than say $1200 it would be worth the effort.