2nd child TTC...sister pregnant

We have a 2-year-old and got pregnant with her easily. Now we have been trying to conceive our second for 6 months, and still no luck. Our families don't know we are trying. My little sister called me last week (who is not even on a relationship) and is pregnant! I know this scenario is hard for her too, so I'm trying to be supportive, but it's hard for me. She didn't know, and she definitely didn't do it on purpose, so why does it hurt my feelings?!