the marriage entry was supposed to indicate if one or both parties were minors (generally followed but not always to the letter) or if widowed (not always followed especially for widowers tho usually a widow would marry in her married name tho subsequent children might well be under her maiden name) - usually an entry pre 1849 would indicate if one party was of a different parish (if both were then a special licence was required tho these special licences could be issued for other reasons) - some parishes were very good others less so in recording details.

Assuming that the parish reg entry gives you no further clues then if you can locate a on-Island census entry 1851 or later then should give parish of birth otherwise you can work by looking at all possible Ann Mylreas (tho illegitimates can be awkward to find) and narrow the choice to just one or two then hope some scrap of additional info might link one of these - obvious sources are wills, MIs, census entries with other than nuclear family members and as you get later in 19th C newspaper articles etc