Taken from Fressingfield parish register
Martha and Lucy twin daughters of Thomas and Elizabeth Vincent late Brundish baptised 24th Jan 1803
Some siblings:
Elizabeth 28th November 1784
Mary 19th Feb 1786
Thomas 15th July 1787
Mary 11 April 1790
William 28 October 1792
John 12th April 1795
James 28th Aug 1797
Sarah 2nd Feb 1800
George 1st March 1807
However; there are several Vincent families baptising children at this time e.g.
Hannah d/o Robert and Mary Vincent late Chambers - privately baptised 30th May 1804
Martha d/o John and Maria Vincent late Pritty - 14th August 1808
I looked backwards and forwards through the register and couldn't find another Lucy; however this is not conclusive as:
(a) I also couldn't see a baptism for a David s/o Thomas and Elizabeth but there evidently was a David as he is later buried at Fressingfield.
(b) I looked at the marriages to see if perhaps one of the Lucys had married prior to 1841, 1851 and her father was named, thereby eliminating her from the puzzle. I did find a Lucy Vincent (minor) of New Street, Fressingfield marrying a Lewis Rowe (minor) of Fressingfield on 7th November 1837. His father was named as Nathaniel Rowe, baker, unfortunately her father's box was left blank. The witnesses were Thomas Vincent and Robert Vincent.
Not sure if this raises more questions than it answers but personally I would be cautious about assuming there is only one Lucy.