She may have already laid her eggs before being introduced to your tank. Since it lived this long, acclimation does not seem to be the problem but be sure to allow 3 hours of slow water exchange when acquiring one that has been shipped or the LFS water is different from the water in your aquarium. The PH of shipped animals is almost always significantly different.
I suspect you received a senescent animal but when you mention tank parameters, please give the actual numbers for salinity and PH as there is a recommended difference for salinity (lower for fish than for corals and inverts). Also confirm 0 nitrites and ammonia. Either of these not being zero can cause senescent like symptoms and death. Nitrates are less I important for an octopus (not so for many corals).
I think @Jocco meant, avoid star fish but consider serpent/brittle stars (correct me if I misinterpreted, Jocco)
I suspect you received a senescent animal but when you mention tank parameters, please give the actual numbers for salinity and PH as there is a recommended difference for salinity (lower for fish than for corals and inverts). Also confirm 0 nitrites and ammonia. Either of these not being zero can cause senescent like symptoms and death. Nitrates are less I important for an octopus (not so for many corals).
I think @Jocco meant, avoid star fish but consider serpent/brittle stars (correct me if I misinterpreted, Jocco)