Yes, she will need an actual visa issued by the US consulate because she's not a Canadian citizen. I can't see why they would be interested in her PR card, but they will want to see the marriage certificate.
It's not a particularly wise idea for a Canadian PR to spend significant time outside of the country. The CRA considers a claim of permanent residence to be exactly that, so she must file
taxes as a resident of Canada. If she doesn't it can cause problems later on.
How the tax laws work is that your spouse and you must file taxes in the same country. She has a residential tie to Canada because of her PR status. You have a residential tie to Canada because she is your spouse, so you must both file taxes as residents of Canada.
This isn't necessarily the end of the world, you can simply file as residents of wherever you live in Canada and file as non-residents of the US while you are in the US by filing Form 1040NR and 8840 every year, have a read of:
http://www.cra-arc.gc.ca/E/pub/tg/p151/README.html
However as Canadian tax rates are higher than US rates, when you claim the foreign tax credit for the US taxes with your T1, you will have to pay the difference between the US rates and the Canadian rates, so effectively you will pay Canadian taxes in total.
The other problem is that if she violates the residency requirement (i.e. spends too long outside of Canada) she can lose PR status and getting it again can be hard - however two years should be okay.
Steve.