What is the advice for a sister who lives in a foreign country and has decided to wear the khimar, taking into consideration that the questioner does not know what she means by khimar, whether it is that which covers the face or the hijab that only covers the head?

If the term "khimar" refers to the head covering, then it is an obligatory religious duty by scholarly consensus. As for covering the face, it is a matter of scholarly disagreement, with the preponderant view being its obligation. It is not permissible to neglect it unless the woman fears an unbearable harm, in which case she is allowed to uncover her face to avert hardship.