It would be similar to (for example) graduating with a degree in Sociology then deciding you want to get a degree in let's say Elementary Education. Some of your credits will transfer toward your new degree as you take the courses designed to fulfill the degree requirements. It of course would be ideal if her present school had a nursing program so all of her credits would transfer. Usually schools will only transfer up to a specific number of credits, demanding that the last 30-40 credits be taken at the degree granting institution.
Since she had a bachelor's degree already, she might want to go through a Bachelor of Science in Nursing program (another route would be to get an associate degree, but we'll skip that for now).
She should first, locate the colleges and universities that she would like to attend.
*Go to their website or call the admissions office to see if there is a nursing program at the school.
*Find out what credits will transfer and what the pre or co-requisites are for the program.
*Determine if there are any essays, interviews, or exams (e.g. mathematics aptitude)required for the application process.
That I know of, there is no special program, but a degree in psych should have given her many of the pre-requisites she needs. She may be able to finish in 2 years.
Best of luck. Any questions, feel free to post.