Hello again Joseph,
I've checked a few things again this morning. Henry Magill/McGill and Mary McKeating had several children in Hutchesontown in Glasgow. The first one I've found was Henry Magill born in March 1876, then Isabella Magill in 1878. During this time they were living at 79 Mathieson Street. The wedding date for Henry and Mary was also given correctly, as is location (Belfast), so I am certain it is them. The next child in this location that I found was Rose McGill, born in February 1882. Then, Helen McGill born on Feb 7th 1885, and lastly Martha McGill born on July 7th 1887. For all children, parents and date of marriage are correct and at the time Rose, Helen and Martha were born they were living at 121 Mathieson Street.
My great great great grandmother Belinda Rougier (married name Davie/Davey) lived on Mathieson Street too. Her original name was Bridget, she was born in Dublin and married James Davey there in Haddington Road Church, with her mother Honor Rougier as a witness. Their first son died shortly after birth. He was James Davie/Davey and he was baptised in Haddington Road Church as a Catholic. One of the witnesses was Martha 'Rougere'. Next, Bridget/Belinda and James moved to Belfast. Their second child, Frances Louisa, was born in Belfast and baptised their (Catholic). One of the witnesses was Isabella 'Rouser' and Bridget/Belinda was noted as 'Bridget Rouser'. It is definitely our Bridget/Belinda, and we can trace Frances Louisa later in Scotland. Isabella(m) 'Rugier' was baptised in 1821 in Dublin in St. Andrew's, parents Frederick and Honor (Fredericii and Honora), the same parents as Bridget/Belinda. In all, given the birthplaces, parents and especially the connection with Mathieson Street, I'm pretty sure that your Isabella and my ancestor's sister are one and the same family. Family folklore from my grandmother was that the family was French, and spoke French. I only found out about the Irish connection when I started researching our family tree. Bridget appeared in the second Scottish census she was in as 'Belinda'.
There are some other threads on this topic, some I see you already know about. In another, one person whose ancestor was Rose Magill told me her family folklore was that the Rougier family came from Rouens - I have no idea on this as yet.
A long message - hopefully interesting.
Regards,
Fiona