As a nurse in recovery - and yes I have spent 4 years now in Diversion - testing following what at times are unreasonable rules and regs, false + etgs and the like - I would advise that you brother or you contact the state board where you SIL is licensed and report her immediately. This is not about family loyalty! This is about the safety of the patients she is caring for. She will be forced into treatment of will have to relinquish her liscense. Harsh I know but it may be the wake-up that she and the whole family needs to accept that there is an Elephant in the living room.
Face facts that eventually she is going to die or kill someone else. How will that feel on your conscience if you do nothing - be prepared for familial backlash!
I used and drank for over 30 years became a nurse and flew under the radar for two years I was never caught or turned in, but after a failed suicide attempt I turned myself in to the board. Why? At the time my husband felt my job was more important than my getting sober. Look for my story on this site - Anyway on Sept 28,2008 I will be four years sober - I am a better nurse, better wife, better mother for the experience.
Good luck to you and yours
Hppy