Not sure how to feel

So my DH and I have been trying to conceive for about 3 months now. And now for the past three months (since I told my sister we were trying to start a family) my sister has been posting how depressed and upset she is hearing about everyone having a family and how she will never be a mom. She has posted how she doesn't matter and how no one would miss her if she was gone. I don't know how I should bring this up to her but I feel that she is being unfair. She is in a relationship with a great guy who has 2 wonderful boys. And she is only in her early 30s. As I said I want to have a family but I'm afraid if I get pregnant then she might kill herself (she in the past has cut herself). What should I do?!?! Am I wrong to feel like she is being unfair?