Before she can get carer's allowance, her son must be in receipt of a disability payment. I realise that Scotland has recently changed the name of the payment but I believe he has to be in receipt of an award and she must give care for at least 35 hours per week before she is considered.
Whoever makes the call has to be prepared to stay on the line for quite some time.
Her other option is to contact a local Welfare Rights Officer, usually listed in the directory or maybe a library could assist with contact details. Hope this helps.