You can order this marriage record online at www.gro.gov.uk/gro/content
This information came from FreeBMD: marriage the quarter of Dec 1879 (meaning sometime between sept 1 1879 and Dec 30 1879) The gro index number is vol 2c page 431 You will need this information to order.
You pay with a credit card.My VISA card charged me a 3% charge over the current rate of exchange, so check with your credit card company to see what they will charge you.I got my marriage and birth certificates for a total of about $12.00.I had them in a week.
The marriage certificate will tell you the father's name and father's occupation.
Once you know her father's name then census records can be searched to determine where else they may have lived.I didn't find any births for an Emily Allen or Emily Florence Allen from 1855 - 1860 in Whitchurch.I didn't find any Emily Florence Allen's born in any location for this date range.There are a lot of Emily Allen's though.