Hi
I looked for other Hill marriages around that time, in case Rachel's siblings cropped up.
On 8 Apr 1864 in St Peter's CoI, Dublin, there was a marriage of Jacob Hill, Gardener, of Lower Kevin Street, son of Richard Hill, to Ellen Hannan.
There is also the marriage of a Joseph Hill of 29 Pembroke Road, again son of Richard Hill.
All three are strong biblical names - could they be siblings? It might be worth checking them out as you may get a lead here.
I noticed the Death of a Richard Hill, age 77, on 7 Apr 1861. Apparently this is in the Clontarf Church Register. As Clontarf is close to Donabate, could this be Rachel's father. Have you checked the Register to see what it says.
Regards
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