No, no need to feel guilty, tigger.
Your Mum will have a reason for wanting to go today which probably has nothing to do with you. It will be for herself. She will tell you later, perhaps. She maybe asked you to go along in case she felt you might be put out by finding out she went by herself.
But if she says later that she was put out by you not wanting to go, you can say she didn't actually say that. If you don't know the full story, you can't be blamed for your actions & there is no need to feel guilty.