Hi
Unless she was under age on her marriage (the age of consent was 21) she would need to be at least 21 to not need parental consent (which if she did may be specified in the church banns book, if it has survived, if the marriage was by banns or on the licence).
Have you found her still alive on any censuses? Have you checked the marriage register for any other Goater marriages?
The marriage according to the IGI occurred in Newington Southwark not Lambeth
MARY ANN GOATER
RICHARD JAQUES
Marriage: 16 JUN 1816 Saint Mary, Newington, Surrey
Marriage coverage of the St Mary Newington registers on the IGI is 1813-1837. Coverage of baptisms is for the same time frame.
The IGI has this marriage
BENJAMIN GOATER
DINAH SIMMS
Marriage: 31 MAY 1785 Alverstoke, Hampshire
This baptism would seem to indicate the couple moved from Hampshire
Diana Goater
Christening: 05 FEB 1794 St Mary, Lambeth, Surrey
Father: Benjamin Goater
Mother: Diana
St Mary's Lambeth has very limited coverage on the IGI.
Regards
Valda