Hi,
I think you might have to get the marriage cert. for William FOOT and Elizabeth J DIMENT to be sure about who she is. The 1939 register shows her DOB as 1878, this wouldn't fit the info for Elizabeth Jane HALLETT/DIMENT.
The 1890 marriage is not John DIMENT to Elizabeth HALLETT, the names with the marriage ref. Dec Q 1890 Bridport 6a 665 are,
Sarah Ann COOPER
John DIMENT
Elizabeth Jane HALLETT
John NORTHOVER
I found this marriage notice,
Bridport News 19 September 1890
DIMENT-COOPER -Sept. 11 at the Registry Office Bridport, John DIMENT to Sarah Ann COOPER both of Morcombelake.
They can be found in Whitchurch Canonicorum in 1891.
Looking at family trees online they have the 1890 marriage is John NORTHOVER to Elizabeth Jane HALLETT, they can be found on all the following censuses as John and Jane NORTHOVER with children that the GRO site shows have the mmn as HALLETT.
I found this info about the 1931 marriage,
16 Feb 1931
Cerne-Abbas, Dorset
William FOOT
Marital Status: Widowed
Marriage Age: 55
Father: George Foot
Elizabeth Jane DIMENT
Marital Status: Widowed
Marriage Age: 52
Father: Arthur DIMENT
I can't see the image to check if Elizabeth DIMENT's father Arthur really has the surname DIMENT. If he is then an Elizabeth Jane DIMENT would have to have married another DIMENT, I can't find that anywhere

There is another tree online that shows an Elizabeth Jane BOLSTER born 1879, father Arthur married Hamilton DIMENT in 1904, he died in 1918 and then in 1931 she married William FOOT. I have looked at Hamilton DIMENT's service records Elizabeth lived in Cerne Abbas in 1919 which would match with the 1931 marriage place.
I'm sorry but I don't have any more time to confirm or discount this idea, it's very late now and I need to sleep

Regards,
Daisy