-Honestly I would ask CBSA directly.
-If she is doing the COPR/landing formalities and then returning to USA (what is informally called a 'soft landing' here), then there is no need to do ANY formalities about goods you are bringing later.
-The reason is that CBSA understands that arriving to do formalities is NOT the same as actually arriving to 'settle' (the test they use for purposes of the 'bring your personal goods' exemptions).
-Hence can arrive with the docs (and other 'goods to follow' per the forms) when she actually arrives to land in Canada. (Side note: make sure which date she chooses to arrive permanently and document that well - it will have some impact for reporting and other taxes paid when she does annual taxes later).
-You can ask CBSA direclty about this to confirm, of course. My understanding is that they actually do basically answer questions like this over phone.
-That said, there are no duties on cars manufactured in USA/Canada/Mexico (you must check the actual place of manufacture and treatment, it is not as simple as manufacturer; I think they will usually go by the place of manufacture on the door plate/docs - there's info out there on how to find out/confirm this is true for your vehicle).
-That leaves GST/HST/PST - I think those need to be paid on all cars imported anyway, but not sure about case for those arriving as new PRs i.e. 'settling.' (My googling skills are weak this morning)
-There are some other special taxes (excise), I don't know about those.
My point being, you may end up finding out that you have to pay GST/PST anyway, and that there are no/minimal taxes you have to pay as a resident.
Note, this is my best understanding, please check
Cars That Look Like Jeeps carefully.