My Degu

Question
I had two degus who were sisters and one of them died xmas 2005 and then decided to replace the one who had died with another so that the one remaining had a companion.
I ended up getting two sisters from a rehoming centre.
On New years eve I lost one of these sisters after being up all night nursing it.
Two weeks later, the one that had lost her sister started fighting aggresively with the original one and it drew blood so I had to part them. I took them to the vets several times to find out why after a year they would start suddenly fighting like this. The vet examined both and we tried anti-biotics in case she had an infection or was experiencing a hormonal problem.
This didn't work and the vet agreed that we would not be able to put them back together again, even though I perservered and tried to reintroduce them, mixing their bedding etc but she was still aggressive.
I am able to stroke her and she comes to me for attention but she will not accept the other degu.
Last weekend I went to a rehoming centre to get two more, one to mix with each of them. The lady had three and said that she had found that putting them all in together had worked before without introducing them and thought that the aggresive degu may be ok as the other three might take the attention off the current one that we have.
I tried this but within minutes the eggresive one drew blood from the original one and I had to quickly part them and then it started on another. Again I parted them and in turn it fought with both of the other two. The last one left in the cage was actually thrown out or jumped too high and I ended up catching it only to be bitten.
I have had degus for 8 years and have never known this to happen before. They have always accepted other degus and I would like for somebody to tell me why they think, this has happened? I would like an answer and perhaps somebody to tell me that she may mix with others in the future after she  has got over whatever is causing this. Maybe it is part of the grieving process after losing her sister that she was very close to?? I am guessing at this as I don't understand at all why this has happened.

Please could you give me an answer or tell me who can?

Thanking you

Margaret Browning

Answer
Hey Margaret, its not that the original degu is grieving, its that degus aren't the most social animals. You would think that a girl-girl pair would work, but it doesn't. I had two degus a boy , and a girl, they were great together, but then the girl died, we still have not bought another degu, but have been told that degus do not work with the same sex well. Try getting a boy degu if you want your degu to have a friend, but remember be careful because degus are extremely territorial.