Jay Jay,
My MIL still hasn't asked me how I am after losing our baby and I even saw her today. Its all just 'fluffy' talk with her, I think its because she doesn't know what to say to me. Maybe that is your SIL's issue too... she didn't want to be told bad news or make you sad so she pretended nothing was amiss. Just keep on smiling with the thought that your baby is thriving inside of you when you feel ignored and of course chat here.
take care, Curl