It's probably come up before, but transliterating English into Japanese is really tricky because Japanese just flat-out doesn't have a lot of English phonemes, so you get... the analogy that comes to mind is a hash collision, actually. You have two English sounds that map to the same Japanese one, most famously "r" and "l", which makes things kind of awkward. If you're an ESL translator it's probably even easier to transliterate a word incorrectly, because English orthography is a mess even on a good day.
The example that comes to mind is FFVI, where Ted Woolsey managed to translate "Ultima" correctly (or at least as correctly as we now understand it to be), while also seeing the
exact same kana in another place and deciding it said "Atma".
For another example, Japanese does not natively have the "ti"/"tee" sound. The workaround is using the "te" syllable, but adding an extra "i" in smaller case to approximate "ti". Hence Ultimecia being spelled アルティミシア, where the ティ in the middle is distinct from the テ in Ultima's アルテマ, despite sharing the same katakana symbol.
Hence why I'm also sympathetic to the idea that Ultimecia was supposed to be Artemisia. The former would have been written as アルテミシア if the text wanted to be consistent with Ultima. That it's not implies it's supposed to be a different name.
The problem is all of these names are made up, so they could use any combination of the Japanese kana syllables to represent any type of English spelling, and I can't say they're wrong. As mentioned, there's a certain way the writers would have written it if they wanted consistency, but that requires the writers to care about being consistent with previous made up words.
Consider that Final Fantasy is the game series where the basic healing spell has been
consistently mistranslated ever since the very first game. It's not "Cure", it's "Care".
At a guess, this is a translation error? Edea seems to have gone to great lengths before her possession to make sure she herself never knew where Ellone was, so this is more "Ultimecia was inevitable, so the best I could do was make it happen in favorable circumstances" I guess?
It might be due to the phrase 私自身, which the translator read as "mind". As in Edea surrendered her heart (or soul, or whatever is the suitable word is for 心; same idea, so not a big difference) to Ultimecia, which meant as a consequence Edea would lose her 私自身.
Now, 私自身 is more literally translated as "my self". Which can be "myself", or "my sense of self" or "the concept that is the self that I have". The translator decided to translate it as "mind", which isn't wrong as such, but might have caused the confusion.
Taking Edea's line into context, my interpretation is Edea "knows Ellone very well" (stated in a previous sentence), and so the best way she can think of to protect Ellone is to surrender her heart/soul to Ultimecia, resulting in losing her self. Which means Edea's body as a vessel for Ultimecia
also loses all knowledge Edea has of Ellone, since it's stored with that "self". Ultimecia can't access Edea's knowledge of Ellone, because Ultimecia is just possessing Edea's body, without access to her personality and mind.
