She already has a BScN from India. She has to do a 4 yrs bachelors degree again in Canada to get an RN?
It is possible that she will have to do a 4 year degree in Canada to become an RN. But, it depends. She has to have her education assessed by NNAS ($650 USD) and it is 99% likely that they will state that her education is "non-comparable" to a Canadian nursing education (I was educated in the US and my education was also deemed non-comparable, although about one year after my education was assessed they made changes and now most US degrees are comparable or somewhat comparable").
If her education is deemed non-comparable, she will still apply to the licensing body (let's use Ontario as an example). CNO, as the licensing body, will either: a) ask her to submit proof of recent nursing work experience (must be within the past 3 years) and job descriptions. From there they will decide it suffices or that the applicant needs to prove more (this is the most likely outcome with nursing work experience from India).
b) ask her to register for the IENCAP ($500 CAD) and successfully complete that exam. It is difficult to get a seat in the exam and can take around 4 months to get a seat and about 6 months until the exam date. (Even with a US education, I had to do this exam).
If she is successful with the IENCAP exam then they will review her courses from India and together with the courses and the IENCAP results, determine if she is eligible to write NCLEX-RN, which is the national licensing exam. Then if she passes this exam, and meets the other criteria (completion of Jurisprudence exam, proof of english proficiency, proof of citizenship or permanent residency, criminal reference check and health fitness to be a nurse), she can apply to CNO for a license.
Is there no way to use the Indian BScN to get admission for Canadian MScN or MN?
Nursing programs are entirely separate from licensing and having a MScN will not automatically allow your cousin to become a Registered Nurse.
Each school varies in terms of their admission requirements and it is highly unlikely they would accept a nursing degree from India when they have so many applicants who have nursing degrees from Canada.
* I should add that if she does not pass IENCAP (you can only do the exam once) or if after reviewing her IENCAP results and her coursework from India, the CNO decides it's not enough to meet Canadian nursing competencies, they can ask her to take some courses (this would occur only if she did poorly in a few specific nursing competencies) or ask her to take her entire degree over again in Canada.