score:15
It's apparently a mystery. Cursory googling using the date tools suggests that the quote attributed to her began to appear out of nowhere in Facebook's early days, and it has been a mystery ever since. See e.g.:
https://adamnathan.com/2012/11/18/alexandra-k-trenfor-john-galt/ (which you've noted too)
http://rogerneill.blogspot.com/2012/12/#4225229763618250907
There's even a journalist who tried very hard to locate her in 2014:
Google Ngram further suggests it's a pure internet thing, in that it fails to find any trace of Trenfor in books until 2000.
Someone with a bit more time might be able to track down the quote's very first appearance on the internet, and ask that post's author directly. It appeared after Google was a thing: the only references prior to 2008-ish appear to be webpages that send wrong last modified date information.