I searched the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds B4 1840 are increasingly sparse, B4 1800 rare. I only search the existing database.
Mayhooth doesn't appear to be either a parish or townland in Meath. It may be a placename.
For Margaret Smith (+variants) B ????, I found 414 B rcds in Meath for all time. Since you failed to specify a date, I will use a range from 1833 +/- 4 yrs. In this range, there are 63 B rcds. Will leave it to you to winnow this down by eliminating false positives.
Google the Foundation's name to lead you to this database. Pls post your search results to my genforum msg.