In your dream, your replacement represents a particular part of your thinking. Because she is a foreign student, then this thinking is new and somewhat strange to you. Consider her personality as you know it. The traits you see in her are the same ones within you that the dream is addressing. Is she shy/outgoing, adventurous/reserved, etc.?
All the people who are not noticing you symbolize your sense of 'loss of self'. Is it possible that with someone from a different culture around, a lot of attention is given to your exchange student. While it was cool and interesting at first, feeling like too much attention goes her way may be getting the best of you. But, besides this, look at your life and see where you may have gradually changed how you think. This would slowly take up residence in your mind where it would, if not kept in check, 'replace' your usual line of thinking. Hope this helps you in some way. God bless.