[Kaderin Triste]

Did she call you Shamus before? Because if so, she is not "having a hard time with this", she is being incredibly and deliberately rude and disrespectful.
Because if I found out that a friend's English name was different than the "foreign" one the introduced themselves as and I had been calling them, I would still call them by the name they introduced themselves as. Although I might, out of curiosity, inquire about their name preference in the "why x name instead of y name" type.