It really depends on what you are planing on doing with it....I gave my 1 to a buddy, and he runs IOS5 without issues...He uses his iPad for web surfing, and a little drawing...He is not a gamer, nor does he use Pages or Numbers.
I still use my iPad first gen every single day multiple times a day. Pages runs great on it. Infinity Blade II is a little slow sometimes but it manages to play smoothly most of the time. Web sites are great. The general OS is also fine and smooth. Still waiting for a breakthrough feature(and a budget) to upgrade to a newer one.
For what I need from an iPad, my iPad 1st gen is great with iOS5. Web browsing, apps, pages, note apps, etc...Right as rain! I don't do heavy gaming, but I am positive the newer iPads will run the games smoother no doubt, but maybe your mom won't be playing heavy games either!
I think you should get the refurb iPad 2. The price difference for the base model is what, $20? It's absolutely worth the extra money for the increase in performance. And it'll be much more capable of running iOS 6 if interested when it comes out.