With "carpetmunching" and "red carpet" being some of my key themes lately in political and other conversations, I had to trace them back to their sex-related origins. As I Googled the Web, I ended up coming across the following Wiki on sexology, maintained at a voyeuristic site.
Voyeurweb's Wiki about Sex
It describes carpetmunching as "lesbian oral sex" (no surprise there) - and links to an article entitled "eating pussy" for more information. Although that latter article can describe any type of cunnilingus (lesbian or hetero), its example photos are indeed lesbian. The examples include the "69" position (where both parties have their mouths at each other's genitals, something I envision Sarah and Kirsten to indulge in early on), the missionary, and more.
The wiki, though written from a porn perspective, does have some good pieces of information, including how the size/shape/position of the clitoris can widely vary between different women, as well as info on public nudity and exhibitionism (both of which I've already associated with Sarah).
Again, the key is to make Sarah and Kirsten very human, rather than stereotypes or ideals, and that indeed does mean developing some detailed, realistic sexuality. This will take a bigger twist given Sarah's ever-changing body and gender transition. And again, I also need to have a good idea on how Sarah looks and functions pre-op (I've already mentioned her enormous "big clit" several times) and post-op (I don't expect her to go through additional labioplasty, which leaves her with minimal labia, but I do expect her to still have sizable clitoral tissue and reasonably deep vagina, and aside from inability to have multiple orgasms, function very well).