i like the visual setup. chains on a statue does seem unique.
here are some questions that come to mind --
(don't get me wrong, these questions are merely to try and find some idea to latch on to -- not actually questioning the setup itself)
1) Are the chains actual chains? Or are they simply part of the carving to look like chains (i.e. are they part of the stonework, or are they real chains that were put on the stonework)
2) Is it possible that this is not a goddess, but the placement just makes people of today think it is/was a goddess? (i.e. is there even the possibility that it is just someone turned to stone, etc. or do you firmly have in mind that it is a goddess?)
3) is it possible that this is not a temple, but rather a simple room/structure that has worn away with time leaving what appears to simply be ruined walls and so someone assumed (based on the presence of the statue) that it was a temple of some sort?
based on the above questions, a couple random thoughts popped in to mind ...
-- Maybe it's not a temple but was one time a simple structure prison. The statue was once a person. Some ancient culture had this woman who did something really bad -or- she was a 'witch' or whatever. and so her punishment was to be isolated (on the island), imprisoned (in the prison), turned to stone (the statue), and manacled (the chains). This would be a rather harsh penalty so you'd have to have it firm in mind what her 'crime' was. To an uninformed person looking at the scene centruies later, it might very well look like it was a shrine in a building, thus the appearance/assumption of temple
* maybe the island was at one time connected to the mainland. but this primitive temple caused lots of superstition and was considered cursed (bad things always seemed to happen to those who visited or were near it). So some powerful magic was done to separate the temple grounds in to it's own island and break it away from the mainland. So, anyone who visits gets some sort of magical curse/badluck.
* maybe it is a temple to a goddess of slavery; maybe it is a temple to a god of slavery who believes that the depicted race (who happens to be shown as a woman) should be in servitude; maybe it is a goddess whose legend tells that she was at one time a prisoner but rose to godhood so the statue depicts her time in captivity as a reminder to those feeling the pressure of life that anything, even the heavens, is possible and not to give up hope.
* maybe the statue isn't important -- it just serves as a fancy altar to showcase the manacles -- they are a powerful evil or powerful artifact on their own. they suck the life energy out of those that wear it (or something.. the exact nature of them would depend on what your PC mentality is like.. obviously, don't give them something that they would just abuse).
anyway, these are all random ideas (not very well thoughtout, i admit).. but still sharing in case anything sparks a better idea from someone else.