the Elizabeth Jane baptised at St Ewe is from a different family. They have 4 children baptised at St Ewe 1847-1852 and are in Christow, Devon for the 1861 census.
Emily, the older sister of your Elizabeth, was baptised 29 Aug 1848 at St Day, daughter of William & Sally, William a miner, and their abode Wheal Rose. Nothing in that record to suggest they weren't married, but that doesn't mean that they were married.
Saying that, there is a possible marriage in St Agnes 25 Jan 1847 for a William Faul & Sarah Yourin both living at Wheal Rose, her father George, his father Henry, all the men miners, both witnesses surname Faul, both spouses sign with their mark.
Faull is not uncommon in the area. There is a baptism for a William, son of Henry & Jenifer of Wheal Rose, 28 March 1825 at St Agnes.
Think the way to go should be the birth cert for Elizabeth Jane. I suspect that the date of her birth on the death reg is correct but out by one year. If she was born in Feb 1849 her age on the 1851 census would have been 2, not 1 as shows.