Oh my gosh Hayley....that's awful! :hugs:
I can't even begin to fathom what is going through her mind thinking that such a personal, painful event for you is fodder for her Xmas newsletter!
I'm so sorry...and FWIW I don't think you're over reacting at all. After my first miscarriage my father said something similarly insensitive to me (to the effect that he didn't know what I was so upset about...two days after it happened) and it was nearly 5 years before I could bring myself to forgive him and speak to him again.
I just don't know what gets into people sometimes, I think you should email her and get it off your chest but perhaps give yourself a little time to settle down before you send it - the trouble with emails is that it's there in black and white and can be read, and reread and never forgotten
Take care.