Unfortunately, it's not a matter of "if" she hurts someone, it's WHEN. It's a crap situation. You don't want her going all psycho and ruining your life, but it's a terrible situation.
I don't think it's really an issue of 'when.' Nurses hurt people all the time. I don't know if they're high or not, but in many facilities people are getting hurt by nurses constantly.
What it comes down to, I'm thinking, is the quality of facility she works at. I've seen some seriously understaffed nursing homes and hospitals where it seems like the nurses don't have an ounce of concern for the patients whatsoever. For example, a grandmother of mine recently had some stays in a hospital where nurses would wheel in a cart of food into a room to a patient that could not feed themself, THEN LEAVE. The food would just sit there until an orderly came to cart it away, untouched! Every meal. Now, if you got someone fired from a place like this, what good will be done? I don't know if they're overworked, lazy, or stoned, but that place needs as much staff as they can get. I've had a grandfather that was given someone else's medication by a nurse and the error put him into an acute crisis: a pretty horrendous error. I was too young to be told what the attack was, but the point is that it was treated and he survived, and in retrospect, the error probably wasn't something someone should be fired over, in my arguable opinion.
Now, if she works with ICU patients, or in the ED, or perhaps even if she works in an upper end facility which is expected to be providing the highest quality of care: now it's another story altogether, and without a doubt she should be reported and have her license revoked. But if all she is doing is carting around food, handing out pills, giving baths, and taking blood pressures, I don't know if such drastic measures are really in order.
Especially if she works in some understaffed local hospital or nursing home, getting her fired, that will harm more people than any medication error or IV bruise ever could.
I think you need to make a decision on this woman in a utilitarian manner.