I understand from my reasearch that the SPOT II, now that it has gotten through a round of recalls, is far superior to the SPOT I, which per many reviews was pretty unreliable. PLBs have dropped in price and weight so that some are actually cheaper than the SPOT II plus the mandatory yearly subscription rate, and close to the same weight. I personally would rather use a PLB, which uses the DOD satellite network, rather than the private satellite network of a corporation that is having troubles. Plus I really don't want anyone tracking me when I'm out backpacking.

However, for the purpose you want it, the SPOT would definitely be better--especially with your mother willing to pay for it! Just make sure she gets the SPOT II, not the old SPOT!