我的朋友要请我参加她的生日会而我不能去，该如何用英语回信拒绝？

Dear Tina：
I am grateful to you to invite me to your birthday party, I also want to, but recently my body is not too uncomfortable, so I can not come, but Happy birthday to you! I hope you can forgive me!
Yours Kerry

（很感谢你能请我参加你的生日派对，我也十分想来，但是最近我的身体有点不太舒服，所以没法过来，但是仍然祝你生日快乐！希望你能原谅！）

月，日，年

Dear Tina：
Hi, happy birthday!
Thank you for you invited me to your birthday party, I'd love to. But today i am feel not good,maybe i was ill.so i'm so sorry, i can't go to your party. very sorry.
have a nice party time.

yours Kerry

Thank you for inviting me to your birthday party.But I'm sorry that I will not be able to go.Because there is something wrong with my body.I saw a doctor and he told me to stay in bed for some days.Have a happy birthday!

It's very kind of you to invited me toyour birthda