YOU SAID:

my sister is so bitchy and she is vastly annoying

INTO JAPANESE

私の妹はとても意地悪で、非常に迷惑です

BACK INTO ENGLISH

my sister is very mean and very annoying

INTO JAPANESE

私の妹はとても意地悪でとても迷惑です

BACK INTO ENGLISH

my sister is very mean and very annoying