It's only means tested benefits she can't claim. So she will still get either incapacity benefit or ESA, depending on whether she has been switched yet. And she will also get DLA.
DLA has two rates for mobiity and three for care, by the amount she is getting it looks like she only gets one payment, possibly the lower mobility part.
Actually I'm sure she should get more than £140 a week as she also gets child benefit. Not that she needs it if her sons are not living with her.
The best soloution?
Probably to buy a house or two, one for each boy. Live in one, rent the other out and live on the rent from the other. Write a will leaving the houses to the boys, or even put them in the boys names now with a clause that she can live there for X years.
And yes I did check house prices in the area.
w.zoopla.co.uk/for-sale/property/bredenbury/bredenbury/hr7-4tf/?include_retirement_homes=true&include_shared_ownership=true&new_homes=include&price_max=150000&q=Bredenbury%2C Bromyard HR7&radius=15&resultssort=newestlistings&search_source=refine