While I’m not exactly sure what happened to your deceased gerbil, it would seem likely that she was suffering from a severe condition that affected her coordination and ability to fend for herself. Since many conditions could cause this I can only speculate, but stroke, meningitis and epilepsy are some relatively common conditions which would eventually have resulted in these symptoms. I do not think that your gerbil was harmed by the other one.

With regards to how you found your gerbil the morning after she died, it is not as bad as it seems. Mot gerbil owners who keep pairs and have lost one will have experienced this, but probably to a lesser degree. For some reason gerbils gnaw and pull at their deceased companions. This usually results in the owner thinking that they were cannibalizing.

But while its probable that your gerbil did eat the parts of the other one which were missing, she will not have done so until the gerbil was dead, and some hypothesize that this is in an effort to revive the dead gerbil. You probably found that the she was also partly buried – another sign that gerbils respect their dead.

I’m not sure whether it would be a good idea to replace the gerbil. You are right that they are normally very territorial, but your gerbil is still young and may accept a younger female. If you are prepared to house them separately if need be, I think it might be worth a try.