judging from your query it is based on the IGI (the IoM is not part of England except for the mormons) - I have a marriage in Andreas of that date and 8 recorded children in Jurby which would match the marriage date.
As it is likely she married in her own parish and having 8 children (last in 1800) she would be close to 21 at marriage (or possibly even younger but in this case the Marriage reg (on mormon film - see www.manxnotebook.com/famhist/genealgy/ldsfilms.htm) should state she is a minor. There are a couple of possible baptisms of a Joney Kneen that might match - www.kneen.com might offer some help otherwise you need look at wills of putative parents.