A question for those with IF issues?

Ok, I want to ask someone who is dealing with Infertility. I just don't know how to go about talking to my sister inlaw about it. She has been TTC ever since her little girl (4 & half year old) was born. She has even had a failed IVF recently. It is always a hard topic to talk about with her because I have no idea what she is going through and I feel awful for her, so I mostly am a listener since well I would hate to say the wrong thing. Well, my daughter is the same age as hers, and I know it isnt hard for my husband and I to get pregnant, but I had kind of been putting it off, so we could be pregnant together also I feel this huge guilt that I can get pregnant so easily. But I didnt want our kids to be too far apart, so my husband and I decided to try for another and I am now pregnant (with my 3rd, we have an older son as well). She still is yet to congratulate me and wasn't very sincere when she congratulated my husband, understandable. But should I be feeling this guilty about being pregnant, I dont think it right for me to feel this way, but I still feel awful for my SIL. I guess I was just wanting an opinion from someone who is going through what she is, and what I should say to her, or maybe if you have an insight on what she is thinking. And for the record, we are very close and she loves my children like they are her own, I know she is happy for me, but I can't help but think she hates me at the same time.