The English have historically treated Welsh people (Scottish people, Irish people, Indian people, etc., etc., etc.) very badly in the past and to some extent it's understandable that this has left remnants of distrust and bad feeling. I also think people living outside south-east England get really fed up with the way the various regions seem to have been relegated to the "second division".
I do think that, whatever legitimate grievances one may have, to treat a little girl in such a cruel and heartless way is just downright nasty, and if I were Greatnan I would also find it very difficult to forget. She has clarified that she agrees that this nasty behaviour reflects on the individuals involved and not the country as a whole.
Unfortunately there are always malicious, small minded people who take delight in making newcomers feel unwelcome and I expect most of us have experienced the feeling of being an "outsider"at some time in our lives.