Is there any way that she will let you see her bank statement to see what money is going into it?
I helped my dad to fill up a benefit form once (it took hours and I had completed many for other people previously) and he told me that he had no savings, it transpired (thankfully before sending the form off) that he had a generous amount of savings - but he said that it was funeral costs and money that my brother and I could inherit. I nearly strangled him.
Your aunt-in-law may be getting an income but she may think of it as something other than a pension.