Completely get it. I was exactly the same when my SIL announced she was preg, twice during the time DH and I where trying to conceive. I just couldn't be around her, I love love love her to bits, but it was just too much in the beginning. It also happened when my DH's best mate who we see all the time feel preg with out even trying. Gutted. Cried for ages couldn't see her either for a while.
Its hard cause your happy for them, but you just feel so ripped off and it is soo unfair. I can't even explain how devestated I was back then.
Missing out on Christmas is completely understandable. You will have all DH's family cooing over your SIL and it will be upsetting.
Maybe write a letter to SIL explaining how you feel. Explain that you are happy for her, but just feel wronged by the world and devestated. What you wrote above makes perfect sense, so even cut and paste that in an email. You mention that you are friends so she will get it, and she will understand. I bet your DH's family will too. Even if they don't they should respect your feelings anyway.
She will undoubtably be upset that she has fallen and you haven't. I know when this friend told her family she was crying as she knew her brother's girlfriend had just had a failed attempt at IVF. She was gutted that she had fallen and the girlfriend hadn't.
Hugs hun, Its hard