Hi Rob
So glad we were able to help you find what happened to Maria.
I have just checked FreeBMD and found the following death records. I notice that you stopped checking at 1848, but you will see that there is another record in March 1850 in Salford which I have listed below.
Dec 1838 BENNETT William Salford 20 *
Dec 1842 BENNETT William Salford 20 585
Mar 1844 BENNETT William Salford 20 627
Mar 1850 BENNETT William Salford 20 665
It could of course be either of these last two, but from what you say it seems more likely to be the March 1850.
Let us know how you get on.
Marian