I forgot about my mumma's birthday... how can I fix it?

It was at the end of Feb, and recently we had a health scare with my husband, discovered a developmental problem with my eldest son, and unleashed holy hell with my inlaws...amidst all this, my mothers birthday went by un-recognized and i am just sick about it. I have never missed it before, and I wondered why she seemed distant lately on the phone - What can I do to make up for it? She's coming by tomorrow afternoon. She hasn't said anything about it, but I know she's hurt...