I don't know whether you have seen the thread about this family at:
http://www.isle-of-man.com/cgi-bin/interests/genealogy/bulletin/index.pl?noframes;read=511364

- But not specifically about Isabella Margaret Moore.

The Maughold parish register has the baptisms:
Isabella Margaret [daur of] John Moore/ Isabella Kermeen [bapt] Dhoon Church 14 Feb 1864
William Henry [son of] John Moore/ Isabella Kermeen Dhoon Church [bapt] 14 Jan 1866
John [son of] John Moore/ Isabella Kermeen Dhoon Church [bapt] 6 Sep 1868
Arthur [son of] John Moore/ Isabella Kermeen Dhoon Church [bapt] 2 Jul 1871.

Other records may be in Ramsey.

Sue