GRO site
https://www.gro.gov.uk/gro/content/certificates/login.asp (need to have a free account to search)
Will give MMN prior to 1911
1851 Q1 William James Marshall, Loughborough, MMN Hallam
1853 Q1 Thomas Whittle Marshall, Loughborough, MMN Hallam
1859 Q4 Mary Ann Marshall, Loughborough, MMN Hallam
The 1850 marriage in Free BMD has a Harriet Hallam on the same page so that looks likely to be the marriage record you are after?
The same site also does a deaths search which gives ages at death for the years that the old index didn't record:
1860 Q1 Harriet Marshall , Loughborough, age 34
There's also a marriage on Free BMD Q4 1860 for a John "Goodwere" Marshall and an Elizabeth Stevenson (I looked at the image the entry was transcribed from and though its dire and difficult to make out I do think it may say Goodacre)
Neither of the above marriages are turning up in Leicestershire Parish Registers either on FS or FindMyPast so I suspect they were either at a Registrar's Office or possibly were Non Conformist of some flavour.
The Annie G daughter in 1871 aged 14 leads me to suspect that Elizabeth was a widow when they married so Stevenson may not have been her maiden name - tracking her back in the census returns may find out more but I have run out of time :-)
EDIT oh! and Welcome to Rootschat!
Boo