Don't know the specifics for IM but:
- has she attained the LMCC ? If not, she would want to do that. It is a royal PITA, but in the long run in order to obtain an unrestricted registration, most provinces will require her to have it.
- first step would be to check what the RCPSC requirements for IM are. In the US, IM is 3 years, if it is 4 years in Canada she will have to make it up somehow. In some specialties, a year as 'chief resident' will do. In others, they will accept a year of a subspecialty fellowship.
- the registration deadlines for the RCPSC exams are something like 18months in advance. She has to submit all her training paperwork in order to be found eligible to sit for the exam.
- if she has LMCC and RCPSC fellowship, she should be able to get a medical registration in all provinces except Ontario. (The medical board there is run by brain-amputated monkeys, no matter how good she is at fetching the sticks they will throw for her, a medical registration there remains a dream.)
- I have NO idea how the canadian medical establishment will look at someone with RCPSC but residency training in the US and medical school in a third country. Given the shortage of physicians in canada, there should be a decent job for her somewhere.
Note:
All these things are expensive and cumbersome. If you guys plan to stay in canada for the long haul, it is worth to go through the exams. If you toy with the idea of going to the US for the conclusion of your eartly days, you might want to consider something else:
Some provinces like SK, BC, NS and AB allow you to practice on a temporary basis (up to 3-5 years) with USMLEs and US boards alone. You are restricted to positions in medically underserved areas (which can be anything from a suburb of Vancouver to an oil-sand mining outpost at the arctic circle.) If you have to wait for some immigration papers in the US to go through, this can be a good option for a canadian landed immigrant.