Hi
Given that the family were travellers - Mary could have married anywhere
freebmd has 8 entries for Mary Ann Bath marriages between 1871- March 1881 but you can ignore the following ones
1875 Truro as it is on the IGI and her father was James
1877 Greenwich - father was Thomas
1880 Hackney - father was Stephen
That leaves 5. You would have to look at the male names on the same page and then look at the 1881 entries for each male to see if Mary Ann was the wife and whether her birthplace/birthyear tallied