If you say 'who is born', it lets the reader or listener know that she will be born in the story. If you say 'who was born', it tells the reader or listener that she was already born and the story is about something else other than her birth.

The answer above is correct - if she was born in England during the story then it's ok to say "she is born in England" However the "who is" is slightly unnecessary. You can say "the main character is an Indian girl born in England"

Yes, it would sound strange to me also. Maybe they mean that the main clause should be in the present tense. So you could write, " The main character is an India girl who was born in England." I guess it would be fine the way it is if this main character is born during the course of the story (or play? or movie?)