It's a convention that most women are listed in most censuses by their husband's surname, though expecially in the earlier censuses it's not unusual to see a wife listed under her maiden surname, and quite common for a widow to be listed by her maiden surname.
In a legal document, to this day, a married woman is usually named as xxx yyy or zzz, where xxx is her given name(s), yyy is her maiden surname and zzz is her husband's surname.
This is why you mostly get the mother's maiden surname in a baptism record. Here's an 18th-century example: 1748, September 11th. William lawful son to Alexander Leslie of Balnageith in Burncrooks and Mrs Anne Duff his spouse was baptized. Witness Mr James Gray minister. [Rothes Parish Register]
Then the same lady witnesses a baptism: 1753, March 23rd. Anne lawful daughter to Joseph Leslie in Braehill was baptised. Witnesses Mrs Anne Duff in Burncrooks, Anne Fraser on the Burnside, Anne Davidson in the New Land of Blackhall, George Dean in Braehill, William Brember in Braehead. [Rothes Parish Register]
I also have examples of a widow remarrying under her maiden surname, with no mention of her late husband's name. Here's one: Margaret Sang died in 1872 and her death certificate names two husbands, Andrew Watt and James Hay. The second marriage is recorded in three different kirk registers: 1834, 26th June. James Hay merchant in Arbroath and Margaret Sang, widow, residing in Timber Market in this parish were contracted in order to marriage and having been regularly proclaimed were married the 30th June. [Brechin Parish Register]
1834. Contracted May 27, James Hay merchant in Arbroath and Margaret Sang in Brechin. Married June 30. [Arbroath Parish Register]
Brechin 30th June 1834. Married James Hay Merchant Arbroath to Margaret Sang (late Mrs Watt) of Brechin. [Brechin Relief Kirk register]
Because she does not lose her maiden surname, you not only get both (or indeed all) her surnames in legal documents, you also get her full name, including maiden surname, in her own post-1855 death certificate and in her children's post-1855 marriage and death certificates. It's also not unusual for both (or all) her surnames to be recorded in her burial record. And if a widow or divorcée remarries, then the post-1855 marriage certificate should include all her previous surnames including her maiden surname and the surname(s) of her ex-husband(s) and late husband(s). You should also get her full name including her maiden surname in her husbands' 1855 and post-1861 death certificates.