First of all - I'm not an expert! Just a language/name enthusiast.
Going by
Rene's finding of
Eugen being the male name used in Albania, I did some research. According to this page
https://en.wiktionary.org/wiki/Appendix:Albanian_given_names the male names ending in -en are generally feminised by simply adding an -a (on BtN, you'll also find pairings like
Dardan /
Dardana and
Gentian /
Gentiana). The vowel combo -eu- is also used in several different names (e.g.
Teuta), which supports
Rene's finding.
Using these hunches, the feminine form of
Eugen would be Eugena.
However, I think it's possible
Eugenia is also an option, since the -ia ending is used in several feminine Albanian names in the Wiktionary article as well. Albanian was influenced by Latin and Slavic languages, too, which tend to feminise names by ending it in -a or -ia, I believe.
Eugenia is also way more common (in multiple languages) than Eugena.
I also found this article, that lists some more common names (
Amelia is popular, but has a variant Amelja; perhaps Eugenja is also possible?). And apparently, foreign names are on the rise in Albania.
http://www.balkaninsight.com/en/article/experts-concerned-about-foreign-name-hype-in-albania-07-27-2016
Chronic thinker.