How to deal with a family member being pregnant right after going through a loss..

I just suffered my second miscarriage in April after 4 years of trying. As I was losing my baby, I found out one of my in laws is pregnant. I'm so happy for them, but I'm hurting for myself. I haven't been around her, but for the 4th of July, we're having a get together at my mils house and I just don't think I can handle being around her. I'm still super emotional and sensitive. I feel like I can't tell anyone how I feel because they will think I'm being selfish or just expect me to put my feelings aside for the day. I just need advice. Like I said, I am so happy for her, but I'm still really upset about my loss. I really don't want to go to the cookout, but I know everyone will expect me to go. What should I do? Thanks!