The lady said that when she used to take classical singing lessons her teacher would encourage her to sing her i's so they sounded more like ee's. She said the i in Heathcliff is sung as more of an ee because it sounds better, i's are better avoided if possible because they don't sound as good when sung. This does sort of make sense and is the only plausable explanation I've heard so far for Kate's pronunciation but I can't find anything about it anywhere on the internet. Can anyone verify this?
In the meantime, here's Kate in that red dress singing her 1978 classic.