I have actually had very good experiences with Marriott customer service. I left behind a pair of flip flops once and they FedExed them to me free of charge.
I would think long and hard about where the camera could be, and if you are absolutely certain that it was stolen from your room (especially if you left it out in plain sight) then I would contact the property manager again. I would calmly explain what happened, and I would also mention the length of time that you were staying there. The length of time speaks to (1) the amount of money you've just given them and (2) the amount of time housekeeping had to scope out your stuff.
I would not ask for reimbursement but I would just (again, VERY calmly) say that you are going to be in touch with the corporate customer service because you feel very strongly that their staff were in violation of hotel policies. I would also suggest that the manager speak wtih the person(s) assigned to service your room each day. No matter what the mgr offers to you, you still should write a letter; Marriott has an online customer service form, and they DO get read. I have used it several times in the past.
Before you do call, though, try to find a price for a replacement camera. Try to hunt down a good deal-- like at CostCo or something. Then, you can say "I paid xx for this camera and case and memory card....but I have priced replacement items valued at $xx"-- if you can offer the replacement as cheaper, you will come off as more reasonable.
Finally, and I know this sounds bad, but I would definitely play the Eva card. You've been through a lot. You can always say that there were pictures on the camera that you needed for her insurance and that what they have done has really screwed her.
Don't pile it on too thick, but do a bit to appeal to their human side.