You could check your monitor with some control solution and check the result with the side of the bottle of strips. If you didn't get any with your monitor you should be able to order it from the company, usually free of charge (I think).
Next time the nurse is testing you could do a test from the same sample with your own monitor at the same time.
There will usually be a variation, but not as big as what you describe. Do remember though, you are ill and BG levels will swing about due to this. There was also at least a 10min gap between the two tests, the difference in which would be influenced by when you last ate, when you last had any medication, exercise, and many other factors along with being ill.