When should I tell her?

I found out almost two weeks ago I’m pregnant with surprise baby number three! When I say surprise, I mean total shocking surprise. My son is almost 7, baby girl turned a year last month, and now a whole new one! Here’s what I’m here for:

My very, dear, friend has been struggling with fertility issues. She recently had her first loss at about 6 weeks a few weeks ago. I’m absolutely terrified to tell her about being pregnant. I don’t believe she will be mad, or hateful, but I’m so afraid of how much this is going to hurt her. My hubby and I have decided to be happy about this shocker baby, (we used protection FULLY) so I’m not allowing it to take away from my shine. But I also don’t want her hurting. I love her so much, I’m afraid this will make her distance from us (which is totally understandable) the advice I’m asking for is HOW should I tell her? And when? She wants us and the kiddos to come over New Year’s Eve, and she’s going to be soooo curious as to why I’m not drinking lol, will it ruin her time if I tell her then? Again, I don’t care about my feelings towards the situation, I’m worried for her. Sorry for the ramble! And thanks in advance !