I would say, while she's working on her BSN, she should start working. Her job might even offer tuition assistance for getting her BSN.
If she hasn't already gotten into some "get your RN & Master's degree" program (which it sounds like she hasn't), it'll be better if she has experience when applying for a Master's program. Also, I've worked with NPs with no nursing experience, and in ICU, it wasn't pretty.
As for CRNA programs, they require at minimum 1 year of ICU experience.
Good luck to you both!