Letter declining invitation to an event

Dear Betty

We wanted to thank you so much for including us in the group that will be celebrating your anniversary of forty years. What a wonderful milestone, and you are such a wonderful couple.

Unfortunately we will not be able to attend the party. Our daughter Helen graduates from high school that day and we will be spending our time with her.

I promise to call you soon, though, to see if we can get together for dinner to celebrate your anniversary and raise a toast to our new college student.

Sincerely
Mia Falcone