Hey, don't feel so bad - it CAN happen. Maybe not officially, but I have definately had it happen to me (verified by repeat exams by the nurse midwife who felt the same thing!) There are several possible senario's: she could have had some swelling going on, she could have had an undiagnosed latex allergy (have had happen, her cervix would close more with each exam due to swelling,) she could have had less pressure of the presenting part on the cervix - thus causing a reduction in dialation. One thing that would be interesting to see would be to try some position changes to see if more pressure on the presenting part would return the cervix to its prior dialation. I do think a change in head position could possibly affect things too, due to change in pressure, etc.
I don't know the official take - but I do know it happens. I am sorry you had such a hard and frustrating experience. Too many people fault the nurse if things don't go the way they think they should.
We can not make the cervix do anything - we just report what happens. And there is also some human error factor and difference between people too. Maybe with the last exam the MD's response was 5-6 when actually she was a good 7. How many times have each of us had a MD do a totally different vag exam and then we compare with the chart (or experience) and know that their fingers are blind!!!
Hugs, go in and have a great day next shift - don't let this keep you down.:icon_hug: