The cas check goes back as far as you have ever had children in your care, so if you are now a grandmother doing childcare go all the way back to when you were raising your own children. I agree it always isn't the best indicator of whether or not you've ever harmed a child, since it doesn't show if you've ever been reported on only if you been investigated and concerns have been confirmed. however I can totally understand where this mom is likely coming from, especially if this is her first child and the first time she leaving her child in the care of another isn't related. references are generally the better way to go since your parents see you everyday and really have a better idea of who you are and the care you actually provide to children. I would see it as just a personal preference for Mom based on her background working in the field, not necessarily a reflection on you as a person