Willow, I don't think you will always feel the way you do, but I think with your SIL, it is made worse by the fact you know her situation kwim? Maybe the last time she m/c really was a blessing for her but this time she may be feeling differently about it (trying to patch the relationship etc).

I have been incredibly fortunate myself, but I still get the irrits up when I see someone who appears to be having babies willy-nilly too, so you are not alone in that, but I think it is hard for you to completely let go of the immediate thoughts you used to have upon hearing someone's pg announcement when you yourself were still trying. Does that make sense to you?