In 1848 you would be looking for a bapt record (not a birth), and in order to find the right one you need to identify your particular Mary Ann Corlett - there were so many people of the same names in the IOM.

In the mid-1800s this is usually achieved by looking at census records in conjunction with bapts and marriages on the IGI (at FamilySearch.org), and then at the parish register - see "Source Call No." at the bottom of the IGI page which gives the LDS film to view worldwide, or see the film at the MM. And once you know who her parents and siblings were, also look at wills.

For a start, how/where did you find her name and date of birth? Do you know who her parents were?

Sue