You wrote:
” I just couldn’t believe that the Catholic Church would change it, even if it were a questionable translation.”
I’m not trying to argue with you, but it isn’t questionable. The Hebrew word means “young woman”. The “young woman” can be a virgin of course, but that is not explicit in the text. I don’t think that it is wrong to translate it as “virgin” since it appears that way in the Septuagint, but in Hebrew it’s just young woman.
Then why did 70 of the best Hebrew scholars translate it as "virgin" in the Septuagint? Why is a the 10th century masoretic text, and a contemporary usage of the word, to be preferred to the septugint which was written by people who spoke Biblical Hebrew everyday and thought the word meant "virgin"?