As someone who lost his Mum to cancer and who now has an incurable/inoperable stage 4 cancer, I can see this from both perspectives.
You can either go OTT and cut off contact with your friend, or you can take a step back and try to learn from this experience.
You said yourself that outside experiences can be deceptive. However many holidays she is having, your friend is still grieving the loss of her Mum. I know from personal experience how angry that can make you feel with the World in general. Your relatively positive outcome, compared with her Mum's, may simply be reminding her that her Mum wasn't so "lucky". She probably feels bad about what she said to you, but grief can make us all lose a little perspective. "This may seem harsh" would indicate that she was aware that she was being insensitive.
Good friends are rare - but it is true that you find out just who your friends are when cancer or other terrible things happen.
