How interesting.

Starting in 1942 the SS began recruiting female auxiliaries in order to replace men being sent to the front as part of the Waffen (Weapons/Armed)-SS. To give an idea of how rapidly the KL expanded during the war, in 1942 the ratio of guards-to-inmates at Auschwitz was 1:6, by 1944 it was up to 1:23, even after a massive influx of 'ethnic Germans' and Hiwis (who made up approximately 50% of SS camp staff by the end of the war).

Some women were undoubtedly volunteers - but the majority of women who served at Majdanek (for instance) later claimed to have either been assigned to the camps by the labour office, or, recruited directly by the SS from nearby armaments factories. There is disagreement among historians as to how much choice such 'recruits' had in their assignment, even if such press-gang tactics were fairly commonly employed by the SS as the war progressed.

According to one such individual, Luzie H. (who was invalided from her normal job after stomach surgery):

The third time they called me in they told me, 'Today we have a job for you where you won't have to perform physical labor, and if you don't accept this job, then you'll be sent to a concentration camp yourself for refusing to work. And there you'll join the other work-shy riff-raff.

Factories relying on slave labour would also 'volunteer' their female workers in order to ensure their access to camp inmates by providing appropriate supervision. Rudolph Hoess related after the war:

Even with diligent recruitment efforts on the part of the Nazi women's organization, very few women volunteered for service as concentration camp guards. As the need for Aufseherinnen [female auxiliaries] was increasing daily, we had to resort to other measures. Every armaments firm that was assigned female concentration camp inmates was required to delegate a certain percentage of its female workers, who would be employed as female guards.

See: Elissa Mailander, Female SS Guards and Workaday Violence: The Majdanek Concentration Camp, 1942-1944 (either through Google Books, or there are relevant excerpts on JSTOR)

Would there have been any coercion, or was she more likely someone's bright young rising star, sent to Auschwitz as a sort of honor posting? How were staff selected?

Well, whether she volunteered or was coerced - it is not possible to say given how little information is available on this individual, but, it's worth mentioning that a posting to a concentration camp in a menial role was hardly a prestigious position - if only because such a job meant one would likely be stuck indefinitely in a dreary shithole in the middle of nowhere. Had it truly been a prestige posting more women would have volunteered, and less men would have left to go to the front (in the Waffen-SS - who incidentally, paid better).

Are there any good books you all might recommend on the subject of camp administration?

Nikolaus Wachsmann, Kl: A history of the Nazi Concentration Camps. Big book, but well worth a read from beginning to end.

I hope they have good reason to be dragging this old lady through court (I suppose, that I have my doubts).

(edit) Looking more closely at her particular vocation, it is possible this individual was an SS Helferin, who were volunteers, recruited from the BDM (female Nazi youth org), and trained in communications (and 'domestic science', in case they were needed in SS nurseries), then assigned to duties in various SS HQs. This seems probable, actually, given that the job was fairly skilled and would require special training.