When details at the time of christening were temporarily written down to some paper, errors in names appeared, when later recorded to the book. Or complete omissions, if he notes were lost for some reason. It's only human.
That's why genealogy researchers need to follow all he records available, as you apparently have done. Too often beginners pick some birth that is close to the later records.
There is no doubt that Ulrica belongs to the family of Greta and her first husband, as otherwise listed in HisKi:
*28.10.1795 	1.11.1795 	Alaj. 	Skrabb 	Eric Johansson   	Margeta Ericsdr.   	Maria
*27.2.1798 	28.2.1798 	Alaj. 	Skrabb 	Eric Joh:s.   	Greta Ersdr.   	Henric
*10.8.1799 	16.8.1799 	Alaj. 	Skrabb 	Eric Johansson   	Greta Ersdr.   	Johan
*28.9.1800 	5.10.1800 	Alaj. 	Skrabb 	Eric Johansson   	Greta Ersdr.   	Susan:a
*21.3.1803 	25.3.1803 	Alaj. 	Skrabb 	Eric Joh:son   	Greta Ersdr.   	Eric
*8.6.1804 	10.6.1804 	Alaj. 	Skrabb 	Eric Johanss.   	Greta Ersdr   	Johan
*9.6.1805 	10.6.1805 	Alaj. 	Skrabb 	Eric Johss.   	Greta Ersdr   	Jacob
*28.7.1806 	3.8.1806 	Alaj. 	Njemitalo 	Erik Johans.   	Greta Eriksd   	Mats
*7.6.1808 	12.6.1808 	Alaj. 	Niemitalå 	Eric Johs.   	Greta Ersd   	Gustaf
*14.10.1811 	20.10.1811 	Alaj. 	Njemitalå 	Eric Johs.   	Greta Ersd   	Anders
*16.12.1812 	20.12.1812 	Alaj. 	Skrabb 	Eric Johs.   	Greta Ersd   	Helena
*10.7.1814 	10.7.1814 	Alaj. 	Skrabb 	Eric Johs.   	Marg. Eriksd   	Eric

 Jaska
P:S. Tuula K already replied while I was typing.