"Lily Rabanastre" is the result of mashing together the two given naming conventions for Viera, and then truncating the result due to a combination of character limits, trouble with the censor, and preferring to have her go by "Lily" rather than "Galbana".

Her full name is "Galbana Lily (of) Rabanastre"—Rabanastre being her adopted home after immigrating there from Golmore Jungle with her mother, and Galbana Lily being the name of a Dalmascan flower.

As for my forum name... back when I started playing World of Warcraft, I needed a name for my first character: A Blood Elf Priest. So I looked up the names of doctors and found a woman whose last name was Rosenstrauch. I thought it sounded cool, so it stuck with me. That was nearly a decade ago, though I still like the name enough to keep using it.