How do you tell...?

My sister in law recently lost a pregnancy. She was 9 weeks along when she found out she lost it, which was about 3 weeks ago. I took a test last night, and it was BFP. How and when do I tell her?  
DH and I have been trying for 18 months now. Sis in Law got preggers first cycle after her IUD was taken out, so, it was hard for her to tell me. We are close, so I don't want to hurt her. But, I also know she will notice that I am not drinking when we all go to the beach together in a couple of weeks.