My MiL always does but she also wants us to remember hers. Always. My SiL was miffed that we didn't wish her mother's day in her early years as a parent. I had never heard of that. My parents would wish their siblings happy birthday, sometimes their anniversaries, but they didn't wish "happy mother's/father's day" to each other.

OP, if you don't want to remember anyone else's wedding anniversary, don't. I don't. Your Mother does. But why make the choice to think your Mother is weird?