These are the only 2 births for a Cubbon baby with Gertrude as first christian name in Brian Lawson's birth index:

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CUBBON, Gertrude 4 Mar 1885 Douglas 513 CUBBON, William RONEY, Isabella

CUBBON, Gertrude 19 Jun 1886 Douglas 589 CUBBON, John Henry MARSTON, Elizabeth Ellen

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The 1886 born child died in 1887:

CUBBON, Gertrude 18 mos Braddan 23 Nov 1887

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It's possible that the one you're looking for has parents William Cubbon (b circa 1844 Arbory, joiner) and Isabella Roney (b circa 1853 Onchan ) and lots of siblings ( info from 1891 and 1901 censuses)

Jean C