Hi Tim,

When those church members' entries on the IGI don't have just a year or "about", but a full date, they have usually overwritten the original entry from the parish register. To check the entry you can quickly find the film number for Patrick (or other parish) on this list of batch numbers for the IOM: freepages.genealogy.rootsweb.ancestry.com/~hughwallis/IGIBatchNumbers/CountyIsle_Of_Man.htm

Click on the batch number for Patrick marriages: M038241 [1714-1883]. write "Shimmin" in the box at the top and enter. Any of these records will give you the film number for marriages in Patrick in 1835, which is 0106738 [1714 - 1837].
Unfortunately it will give you very little information before the late 1840s when fathers' names and occupations were entered - sometimes a place name, or underage, or widowed, or from a different parish (named), but rarely anything else. Judging by the 1851 census you found, Philip was underage, but that won't help you with Margaret (aged 42 b.Patrick).

Looking at baptisms through that same batch number website (which shows only extracted entries), there is a MARGT SHIMIN bapt 4 SEP 1808 Patrick, Father: JOHN SHIMIN, Mother: ANN GELL - a possibility?

Sue