The RL me lives in Japan, so perhaps I can help.
First, do you have any idea where in Japan the sim owner lives? Even if in the Northeast, for all the horror of the disaster, the numbers of dead and missing are proportionally small, and tt is statistically unlikely that she is dead, to begin with. If anywhere else, she is alive and well.
Second, if her credit card is still active, I guarantee that she is alive and and financially functional. Banks here are every bit as predatory as anywhere else, and they swiftly cut off the accounts of all dead and missing, with polite and regretful bows to surviving relatives. Company balance sheets always win out over human considerations.
Third, those of us not directly affected by the disaster have undergone something of a conceptual shift. Every day the weather forecast includes radiation counts and electricity usage statistics, and even escapist types who enjoy SL have experienced a jolt (though in my case this resulted in me signing up to SL, at long last, but I live in central Tokyo). If your sim owner has children (as I do not), she has reassessed her life priorities as a matter of urgency, and pixel horses, however cute and hungry, must take a back seat, for a while at least.
My conclusion: don't be sad -- the sim owner is almost certainly alive and well, but probably in an area affected by the disaster to some extent, and her mind is on other things. She may return to her hobby at some point, but then again may not. Grieve for the horses, but rest assured that she is carrying on with her life, even if it is less 'sweet' (amai in Japanese, something like 'soft and easy') than before.