Interesting, I never caught this but it is fitting considering the pattern of other characters names like Barghest, Hecate, Sphinx, Echo, Lamia, Camazotz...
If I may hazard a guess as to why he used an unconventional katakana spelling, it's because "arachne" has become a generic word for spider-woman in Japan, like "lamia" and "alraune".
アルケニー (ark-nee) is therefore based off the Greek pronunciation, as opposed to the conventional アラクネ (ah-rak-nay) which clearly came from the English pronunciation. I don't know a word of Greek but putting ᾰ̓ρᾰ́χνη into google translate to pronounce, you can hear that there's no stressed "a" sound in the second syllable, and the word ends with a long "e" sound.
Therefore, the dev is naming the character after the mythological Arachne, not the generic word for spider-girl.
(if this is true I am impressed by his level of detail)