There's no marriage of Sophia Breed on the BVRI at Southill, nor a burial on the NBI, so she must be a possibility. Frustrating that the marriage (if indeed they married) is being elusive. I've been through the Hugh Wallis site to see which Beds parishes between Southill and Wrestlingworth and generally in that area of Beds, have not been extracted onto the IGI in the 1830s, and there's only two that I can see - the hole in Southill which is covered by the BVRI, and Campton, where nothing after 1812 is on the IGI or BVRI. Just to say you've covered all bases, and if you've nothing better to do, it might be useful to check the microfilm of Campton to see if they did make a bit of a dog's leg and marry there.
Southill parish register transcript merely says illegitimate daughter of Mary Breed against Sophia's baptism. There's also a burial of a Mary Breed at Southill on 25 Oct 1812, just a couple of weeks after Sophia's baptism (no other detail on the burial). Now what would have become of a 2 week old orphan - usually raised by grandparents/siblings of the parents. I've never followed how she moved from Southill to Wrestligworth. I wonder...... but here I'm moving from speculation to the realms of fantasy! We don't even know if it's the right Sophia
Regards
David