Am I the selfish one?

Me and my husband had tried to conceive for 3 years. Finally with success. The same day we found out is the same day my SIL got engaged. I happen to be due two weeks before her wedding date. Before you ask she had been planning this wedding from like their second date and they haven’t been together even a year yet. Beside the point. The wedding is in north California in April. Still cold and two week old. Me and husband decided from the beginning that I would skip and he and our older son will be attending. We haven’t kept this a secret and have informed them over and over. Today his mom calls and asks him if I will be going. He said we already said no, not having our two week old traveling, surrounded and it being cold, not going to risk him being sick, this is only one factor. Let’s not forget what happens to our bodies after birth and what our first weeks are spent doing. She actually got mad at him. I’m still irritated that she’s mad. I’m baffled, how could she think this would be a good idea for us ?