How do you tell them??

So me & my bf are trying for baby #2. Recently my aunt(dad’s sister) found out she was pregnant in January and then drs told her that she could possibly lose the baby due to some complications that she didn’t know that she had. So she ended up miscarrying in February. I can see it hurts her still. She have no kids and was so excited when she found out she was pregnant. She always wanted to be a mother. Now me and my bf have talked about baby #2 since our daughter is 5 years told we thought we should give her a sibling. Now I’m not pregnant just yet but when I do how do I tell her knowing her situation? It makes me feel so bad. I had been telling my bf for baby #2 before she was pregnant but he would always say mmm idk. Until he said ok you’re right we aren’t getting younger and our daughter needs a sibling. How would I talk to her( my aunt) about something like this?