Telling SIL who's MC

So my husband and I have been talking about TTC for about 9m. We started 3m ago, right before his sister had a MC. Well I am now 7w and I'm terrified to tell her. She already assumes were trying b/c she was pregnant (not true, I have a 6yr old and 2.5 yr old, I want my kids 2.5-3yrs apart. The timing just happened that way). Well were suppose to tell his family tm and I don't want to. I'm scare of her getting upset an or hating us. Any advice?