Looks as though Margaret married for a third time ...
1881 Census:
PHILLIPS Thomas - Head - Married - Male - Age 45 - Born: Brecon, Brednock, Wales - Occupation: Rt Carpenter
PHILLIPS Margaret - Wife - Married - Female - Age 49 - Born: Longtown, Hereford, England - Occupation: Bread Baker
COLLARD David - Stepson - Unmarried - Male - Age 15 - Born: Tredegar, Monmouth, England - Occupation: Butchers Lad
PHILLIPS Jane - Daur - Unmarried - Female - Age 13 - Born: Talgarth, Brecknock - Occupation: Scholar
Dwelling: 43 Commercial Road, Bedwelty, Monmouth
1342262 - RG11 - 5242 / 67 - 10
FreeBMD has this marriage listed which may be what you are looking for:-
Fourth Quarter 1877
FIELDING William
PHILLIPS Thomas
PROBERT Margaret
REES Jane
Bedwelty - Vol 11a - Page 160
Also there is this death listed:-
First Quarter 1876
PROBERT David - Age 41 - Bedwelty - Vol 11A - Page 79