I will not be singing it from the rooftops when we get any BFP's mainly due to having a chemical and knowing how painful it is to get a BFP and then lose a BFP. I just couldn't imagine having to tell everyone I was no longer pregnant after I had potentially * sung* it from the rooftops and told the whole world. It was hard enough telling DH and my Mother. In saying that though each to their own and Des has every right to sing it from the roof tops if that is what she wants to do
I wanted to add that I guess you need to consider the varying degrees of TTC as well. Some women already have children and then have to use IVF for other additional children. Some TTC for years naturally and can't afford IVF. Others have IVF once and conceive while many have to have many cycles of IVF and then there is the ladies who NEVER conceive or have ANY children. I am not sure which category your SIL falls into but I think these factors could have influenced her reaction as well as the posibility of if she is currently cycling her emotions might already be heightened by all the hormones.