Need advice regarding office politics - Anonymous

I would appreciate it if some of you could share your thoughts and offer advice about how I should handle a workplace situation.  I do MT on site and work Saturdays with one other transcriptionist.  We work on production and everyone's numbers are posted on an internal website for us to view.  Our production is being monitored pretty closely now because there may be staffing cuts in a few months and that is one of the criteria being used to decide who gets to keep their job.  I'm a hard worker and do well but my numbers are only about in the middle of the group.  Right now, I know that quite a few people are padding their line counts by working off the clock and requesting the easy doctors, but that's another story.

The thing that currently has me upset and that has bothered me for several months is what happens with my Saturday co-worker.  She's a very high producer, thinks she's all that (and a bag of chips) and implies that she's certain she'll be retained when they start cutting people.  She knows everyone's production and has on a couple of occasions quoted a co-worker's numbers to me, asking me what she does all day and why don't they do something about her.  Somehow she has also learned how much money this person makes and told me that too.  This past Saturday she pulled the production report up on her PC and showed me the numbers, pointing out one person and saying that they did not belong that high in the ranking, (no names are listed there, every MT has been assigned a number), it could have been me but fortunately it was not.  I got very upset and flat out told her that the only numbers we need to be concerned about are our own.  She did later apologize, I actually think it's an obsessive-compulsive thing, needing to be in control of what everyone else is doing.  I am also a radiology MT and several months ago when I arrived in the morning she told me she wanted me to look up her DEXA scan results.  Of course I said I could not do that, to which she replied "I don't know why I said that."  I let that go but actually now regret not having gone to may manager at the time, as that would have been a HIPAA violatiion.

I have submitted a request to have my schedule changed to Monday through Friday, thinking that it would remove me from that environment on Saturdays.  If I confide in another co-worker, the chances are very good that what I say will get repeated.  Going to the manager makes me look like a tattle-tale, although I'm still mulling that over in my mind.  If she needs a reason for the schedule change, I may still be required to spill the beans.  Hopefully the change will get approved with no questions asked. 

I'm under major stress working full-time, trying to study for a coding cert. exam and looking for new job, it's getting to me!

I'm sorry to be so long-winded.  Any advice or words of wisdom would be appreciated, thanks in advance.