I'm pretty sure they can "administratively refuse" you at the border so you can flagpole. You just say you want to go to the Canadian side. Otherwise get a US visa first, if you are concerned. I have read some stories about people being given a hard time for doing this without a US visa.
She can just make an appointment at an immigration office inland to land, though.
My wife landed at Rainbow Bridge. We've always preferred it over the Peace Bridge because it is typically less busy. Commercial trucks aren't allowed on Rainbow bridge which probably makes it somewhat better.
We drove...we were living in Toronto at the time and that's usually been the place we crossed at whenever we visited her family in the States. We've just always liked Niagara Falls
As you may have seen from other posts here, landing is really no big deal...if the PR application process was the final exam, the landing is the graduation ceremony All they will do is ask some very basic questions (have you committed any crimes...has your family status changed...what is your mailing address), and they will stamp the CoPR and you will be on your way.