Hi,
This is the 1859 marriage,
Saint Thomas, Poole
September 8th 1859
William ROBINSON
20
Bachelor
Seaman
Green's passage
Father: Edward ROBINSON, Coast Guard
Maria HANCOCK
19
Spinster
Green's passage
Father: --- ---
DeathMaria ROBBINSON* Dec Q 1859 Poole 5a 168
Age: 20
BurialSt James, Poole
Maria ROBBINSON*
Poole
October 29th 1860
Age: 20
*note the double B spelling on the GRO index and image and also her burial.
Her death would fit with the William ROBINSON widower in 1861 that you've found.
However because of her age and that there is no father mentioned on the marriage certificate, I think that this could be Maria,
1851 HO107/1855 f.257 p.25 Poole, Dorset
13 Green's Alley
HANCOCK
Thomas Head M 71 Tailor Dorset Steep Hill
Ann Wife M 65 " Poole
Jane Daur U 33 School Mistress " Poole
Maria Grand-Daur U 11 Scholar " Poole
Thomas Cousin U 16 Agl Labourer " Poole
Oddly in 1841 there is no Maria HANCOCK living with this family but there is a Maria BROWN of the right age. I wonder if they are the same person?
I can't find a definite birth for a Maria BROWN or HANCOCK in the right place at the right time.
1841
Perry Garden
HANCOCK
Thomas 55 Taylor
Ann 50
Jane 20
Frederic 14
Aldolphus 10
Thomas 6
Maria BROWN 1
All born in county.
Hope this helps

Regards,
Daisy