Dear May
Thanks for inviting me to your birthday party this Saturday. We have not met for so long, I am very happy to have a chance to catch up with you and celebrate your birthday. Unfortunate, my mother is down with a bad flu. My father has been assigned to work overseas. I am the only family member available to look after her. Therefore I am not able to attend your party. I have selected a very special birthday present for you. John will send the present to you on my behalf. I hope you will like it. Please don't be made at me. I will also find another time to have dinner with you.
Happy birthday!
Yours faithfully,
Lily