Learn English – The meaning and usage of “be against this background”

I believe that in most instances of use, the speaker intends "I am unclear" to have the same meaning as "it is unclear to me," and the speaker uses this phrasing perhaps to be a little kinder to the person whom he/she addresses by way of taking on the burden of the misunderstanding.

However, technically, "I am unclear" means that the speaker is not explaining something in a way that others might easily understand, e.g.,

I am unclear in my presentation about whether the relationship is merely correlational or causal because tests were inconclusive.

In this context, the word above means better than. If someone is above doing something, they feel as though the activity in question is not up to their standards. It is also said that the activity a person is above is beneath them.

This is supported by the fourteenth definition of above, which states:

14) of too fine a character for: He is above such trickery.

In your question, the person negated the phrase. By saying she is not above breaking a rule occasionally, she means that she does not consider herself too good or proper to break a grammatical rule when it enhances her clarity.