Roger,
It's very feasable to use a p-series HT around the house, in the yard, for shopping, etc. I use mine just about everywhere I go. Friends often joke that I never go anywhere without her
That said, I would seriously look at the i-series vs. the p-series for your wife. If she feels completely comfortable on the p-series and will be using it in the house, etc., the p-series should be perfect. But the i-series does add a bit of stability and industrial-ness that you don't get with the p.
As an example, I was playing with a friend the other day, riding his i-series around. When I stepped on my p-series, it almost freaked me out: it felt like I just stepped on nothingness; psychologically, I couldn't believe for a moment that it would hold me up
Of course, I was wrong. The p-series is really an amazing machine. Of course, the whole p-i-e family is pretty amazing.
Chris