Why does "of Ana" become "Anei", but "of Monica" becomes "Monicăi"? Is this because "-cei" would significantly alter the sound of the name itself?
I am not sure what the actual rule is, but yes, it just sounds wrong. It's the same with 'Anca' -> 'Ancăi'. Also, names ending with a consonant and newer names of foreign origin use the masculine article.
Thank you. I just came here to aske why I had Mama lui Carmen in the previous sentence (masc) and now Mama monicai (fem)