The baptism came from Ancestry, they have images of that and of her marriage. Look out for free trials or cheap offers. The mother's maiden name came from the free GRO site.
As to the actual birth date, you may have buy the certificate to get that, unless you can find a record of her death, as some give birth dates, depending on when she died.
Hang on! I've just looked at the page again and further down on 12th Sept 1858 is another entry for her, which has been crossed out and the words "entered by mistake" written in the margin. I guess she was baptised at home as she was expected to die, survived and then had a welcome to the church ceremony in September that was entered as baptism by mistake. ANYWAY that has a birth date of the 1st April 1858!