I am aware of that this is a pretty old thread, but I couldn't stay away since she was an interesting ship even before she became a cruise ship.
This is the following info I have put together and found online.
Well for starters Sea Diamond started of as a "Cruise ship" in Sweden, well she took passengers but unlike most Cruise ships she also had a car deck for around 80 cars.
From what I can see from timeline she was in Finland to be rebuilt into M/S Sea Diamond as a Cruise Ship, however she only spent 1 month there so I highly doubt that they did anything to the car deck. Some visable changes are the rear top of the ship, a couple of balconys and so on.
The car ramp is also visable on some photos that was taken when she was rebuilt into Sea Diamond.
As for someone claiming she was in port or inside a harbour, that's false. As seen on photos and videos of her when shes sinking shes near cliffs but not any port.
She hit ground and sank within 24 hours, the cruise line company stated that the ground she hit was marked in the wrong spot on the charts, according to the cruise line company it was later proven right. According to the chart the ground should have been 51 meters from the coast while in fact it was 131 meters.
"Investigations carried out by the defense team of the Master of the Vessel and Louis Cruise Lines, after a lawsuit had been filed against them, have included a new hydrographic survey of the area of the accident in Santorini. This survey was carried out by Akti Engineering, and discovered discrepancies between the actual mapping of the sea area and the official charts used by the Sea Diamond (and all other vessels) at the time of the accident. The detailed survey claimed that the reef, which the Sea Diamond struck, is in fact lying at 131 meters (429 feet) from shore and not at a distance of 57 meters (187 feet) as is incorrectly marked on the nautical chart. The official chart also shows the depth of the water at the area of impact varying from 18–22 meters, whilst the recent survey shows that it is only 5 meters.
The findings obtained by Akti Engineering have since been passed on to the Hellenic Hydrographic Office of the Hellenic Navy and other responsible authorities, with the aim that the necessary changes to maritime charts should be made and similar accidents to be prevented. According to a branch reviewing source, the Hellenic Hydrographic Office initially rejected the new mapping, but a later study confirmed the findings of Akti."
The above part is taken from Wikipedia where photos of the sinking can be seen too. It also says the following: "It has been speculated that the deep, almost vertical shore of the bathtub-like caldera made it impossible to beach the ship and save her from becoming a total loss."
I hope this is at least something good and I apologise for any misspells in my text, english is not my main language and there can therefor be some errors in it.
Best Regards Alex.