Attendance Allowance (AA) is not taxed and does not need to be declared it can be paid in addition to almost any other benefit, it is like Disability living allowance but for people over 65, the only time it stops is if your Mother were admitted into Hospital or some types of care home, after a waiting period of four weeks.
Your Mother should check to see if getting AA can trigger help with means tested benefits, such as Housing or Council Tax benefit, or Pension Credit if she is in receipt of these benefits.