This can be either due to her age or due to a Lower Back Pathology . Get her to an Orthopaedic or a Neurosurgeon to get her assessed clinically . She should be assessed for her power and sensations in her lower limbs.
Next Steps
Visit to a Orthopaedic or Neuro Surgeon . XRay / MRI of Lumbar Spine
Health Tips
Ask her not to bend or lift heavy weight , Do not sit on floor or lie down on floor ,