Hi Roseann, I had a look at Roots Ireland and see 5 baptisms records, however there are two oddities, firsly the children are born in Westmeath to a John Keegan and an Ellen Keena. Also there are 2 baptisms for a Patrick Keegan and a Patt Keegan both in October 1862 in Castletowngeoghan while the others are in the principal town of Mulligar.
I searched from 1845 to 1875 and all these are between 1860 and 1863, Ellen; John and Mary are the others. Civil registration commenced in 1864 so just too early.
A John Keegan married an Ellen Keenan (assume transcription error or entry error) no other information on certificate, marriage in June 1860. You can see the registers here, parish is Mullingar.
It is possible that the lady was Mary Keena but to distinguish her from her mother she was called Ellen, as in christened Mary Ellen. I tried Ask About Ireland and Griffiths Valuation and unfortunately there are 66 Keena in Westmeath, a lot for an ususual name and worse there are 161 Keegans, no address on marriage entry.
The registers are here https://registers.nli.ie/ You can only search by year and month and then read, all records are in Mullingar except Patrick and Patt. in Castletown-Geoghegan might indicate your Keena is from there and the mother went to her mothers for the birth but this is all leap of faith stuff.
Good Luck,
Pat