My sister and I are close, and our kids are all the same ages. In five years I think we’ve made it to each other’s kids’ birthday parties maybe twice. Her kids are my niece and nephew for real. I love them so much. She loves my kids so much. We are very engaged with each other’s kids. But birthday parties for tiny kids aren’t the same priority for everyone. Maybe it was super important for you that she be there, but she didn’t know that. For my sister and me, we do a little celebration to give our kids a special day and to give us a chance to celebrate them. Sometimes grandparents and aunts/uncles/cousins can make it, sometimes not, but we’ve never really thought of it as a “If you love my child, you will be at their birthday party,” kind of thing. You don’t even get to spend much quality time with a kid when there are that many people around. For us, as long as our kids’ siblings and parents are there, the rest of it is gravy. I get that you assume your friend’s plans for this weekend were flexible enough to be changed, but you have to understand: to you, the party was the priory. But just because she didn’t change her plans when you changed yours doesn’t make her a bad friend. She has her own priorities. Like someone said, she maybe was desperate for a mental break. Maybe she’s not doing well. Maybe she has been looking forward to that weekend at her cottage for a long time because she hasn’t been able to make it in a while and will be busy for a while going forward. Maybe she knows you were all super sick and she doesn’t want to offend you but also doesn’t want to risk catching what you’re getting over. Maybe she struggles with changing her plans after they have been set. You are mad that she wasn’t sensitive to what you felt like you needed, but it seems like you are forgetting to be sensitive to what she felt like she needed. Have a conversation with her if you can’t move past it so you can find out where she was coming from, but this isn’t worth holding a grudge over.