Hi
For that period of time you won't get an actual Birth Certificate as it was prior to the start of Statutory Registration, but you might find an entry in a Church Baptismal Book.
I started looking for another census record, an earlier one when Janet is still with her parents in the hope that it might shed some light on her age and place of birth, and on the rest of her family.
If you can find the death certificates for Janet's parents you could find out more about them, and even get enough details to find them in the census.
There are 2 death entries on SP for Janet Clark, other name Gillies 1855-1910, one in 1855 aged 75, the other age unknown in 1862, Port Glasgow Renfrew.
I looked at the 1861 census, but the first likely one I found was in West Calder and has father Thomas (widower, 53) as a Master Baker, which doesn't match up to what she put on her marriage certificate, so probably not your lot. (If you are interested I can post a transcription of the entry). Out of credits now, but maybe if you post a lookup request someone with free access can check the census recods and get you some more information. It is not always wise to base all your searches on one census entry, they are notoriously unreliable!
Kirsty
