1861 Scotland Census Record shows her as Helen Stewart b 1829
1871 Scotland Census Record shows her as Helen Stewart b 1833
1881 Scotland Census Record shows her as Ellen Stewart b 1832
1891 Scotland Census Record shows her as Ellen Stewart b 1836
Actually, the original census doesn't say that. The census
never gives a year of birth. It tells you the age the person claimed to be on census day. The year of birth is often introduced in what claim to be transcriptions but are in fact interpretations, and by 'calculating' the year of birth by subtracting the age from the census year the answer is wrong three times out of four.
The 1861 says she was 32. Census day was 7 April, so if her age is accurate she was born between 8 April 1828 and 7 April 1829.
This is obviously incompatible with her age as recorded in the later censuses, so she could have been born any time between 1828 and 1836.
William and Helen/Ellen and family are in Liverpool in 1881 and West Derby in 1891. Not in Scotland.
There is a 55-year-old Helen Stewart in Perth in 1891 but she is Helen Nicoll, widow of Farquhar Stewart, and the 1871, 1881, 1891 and 1901 censuses all give her birthplace as Blairgowrie.