Those should be two different conversations. The family night should be an email.
The fact you are dropping the charges should be a conversation.
I guess I'm nutz, but my line of work, I've learned to not put anything in writing that could come back and bite you in the A$$. And there's not one reason to not be careful here. Write out what you want to say and go from there, but don't let her have a record of it.....just in case.
Call her and say:
Thanks for taking my call. (If she doesn't answer leave a message--Please call me when you have a free private moment. I want to talk about the charges....and possibly dropping them.) I wanted to talk to you about the charges. Basically, I'm going to be dropping them and wanted you to know. I don't know if you'll be notified or how that works, but in case you are not, I wanted to make sure you knew.
Take care.
And hang up.