bikash ji yes your brother in law has to apply for immigrant visa for his wife, if he has green card it takes longer time to get visa for your sister, once he get citizen it will take just 9 months to get your sister in america and get green card too applying as students for nursing and apply for immigrant visa is totally differents it does not have any connection either she can apply for nursing course and get visa for as student or wait till your b in law get citizen, u know that your brother in law has to be be atleast 5 yrs as green card holder before applying for citizen with no criminal records and good credit i think its better to apply as student visa and stay with her husband she can change her status when yoour brother in law get citizen and apply for her it is also better if your brother in law apply for her right now a immigrant visa it takes time