There have, in fact, been threads on this before.

But as historians, should we make moral judgements upon the subjects we study? Can we even make moral judgements upon the subjects we study given the nature of our methodology?

TL;DR: You shouldn't.

It's not so much a question of should or shouldn't, I think, since you inevitably will even if you try not to. There is no such thing as an absolutely objective representation of history. In picking and choosing which elements are more and less important, which methodology to employ, whose standpoint is being represented (in the example you posit here: that of the 65 year old monarch, or that of the 12 year old girl?) an implicit value judgement is made which reflects the internalised ideology of the researcher. It is impossible to escape this phenomenon. That is okay, the fact that any representation of history is inherently subjective and incomplete does not mean that it is worthless or that history is fundamentally "unknowable" as some postmodernists claimed. It merely means that the ideology of any historian and the subjective character of the history they're writing should be kept in mind when reading.

I am extremely suspicious of any historian who claims to write "objective" history without any bias, since this only serves to try to conceal the bias and subjectivity inherent in every history. In fact, this can be extended to all social science (and beyond even that).

Hi. I'm not a historian, but I do have a related question.

I think it might be easier not to moralize about evens that happened thousands of years ago, but how does a historian avoid making moral judgments about American slavery, the Holocaust, or other big moral issues that really resonate with us still?

Does the historian dealing with these topics just stick to contemporary reactions and how these things have shaped our way of thinking decades later?