Hi Joanne
I looked through all the dozen or so trees on Ancestry, and the thing which struck me was that not one had submitted an 1841 census for Eliza Clark b 1814.
I saw that in all the 5 censuses following her marriage she's absolutely consistent in giving her name as Eliza (not Elizabeth) and in giving an age which suggests a birth year of 1814.
I figured that since she was born in Douglas, and married in Braddan in 1842, there's a strong chance that she was on the island for the 1841 census.
Brian Lawson's census index for 1841 gives these entries for Eliza/Elizabeth Clark in the correct age range (given that the instruction for this census was for ages to be rounded down to the nearest 5, which some people interpreted differently from others):
CLARK Elizabeth 30 Maughold 1464/7 39 12
CLARK Elizabeth 30 Peel 1463/8 54 36
CLARKE Elizabeth 25 Andreas 1463/1 44 3
CLARK Elizabeth 25 Douglas 1465/7 11 18
CLARK Elizabeth 25 Michael 1464/9 41 8
CLARK Eliza 23 Douglas 1465/8 23 3
The only Eliza Clark on the island was in the John Clark, grocer, household, and in 1851, she wasn't with John Clark and wife, Margaret. The most likely name for John's wife turned out to be Margaret McGuire/Maguire, but this couple didn't marry until 1818. So if this was indeed the household of John Clark and Margaret Maguire, then John probably had had a previous marriage (although Eliza Clark in the 1841 household wasn't necessarily a daughter, since relationships weren't stated)
When I looked through the burial index for a female Clark who died circa 1816/17, I was pleased to see one for a Jane whose maiden name was Scottish, so I checked in the IGI for a marriage of a John Clark to a Jane Ogilvie and found one in 1806 in Onchan. The only baptism of a child born to a couple with these names in the IGI is Ann Clark 1st Nov 1807 St Matt, Douglas (although unfortunately it's a patron submission)
The crucial piece of evidence will be the will of Jane Clark alias Ogilvie. This will either demolish my theory, or confirm this educated guess.
Jean C