Margaret Gallagher is a very common name in Donegal. You ought to try and find a marriage certificate or death certificate to get her parents names. I don’t see any birth around March 1896 in the statutory records for that area (Donegal town civil registration district) and the parish records for that year are not on-line. However this family in the Inver area looks promising:
Bear in mind that people sometimes just guessed their ages or dates of birth and so the baptism date you have may not be totally accurate. You could write to the parish office to see if they have a baptism that fits.