Need help with my female degus

[pagancat]

I have 3 degus, Lucy and Liu are sisters, and Zahra is our other one. All were adopted from our local humane society about 1 week apart (Lucy and Liu 1st, Zahra 2nd) at the end of August. Lucy and Liu are about 4months old and Zahra is about 5months. Up until recently all 3 were in the same cage together, it was a small type hamster cage with the 2nd floor removed and fabric hammocks put in to make room for them. Also they were given "freedom" runs daily for 2 2hour periods in my boys bedroom with lots of stuff to play with and access to a wheel (they chewed the one that was in their cage). All of a sudden Zahra began attacking Liu (Liu is the lowest ranking and smallest, and has never tired to be the boss). So for about a week (that's how long it took to get the newer bigger cage) I had to separate them using the second floor as a divider so they could still see and smell each other but not be able to hurt each other. Now Lucy and Liu are in the bigger cage and Zahra the smaller one still side by side. They even sleep side by side. But can not be an open area together as Zahra goes after Liu and Liu ends up shaking and chirping with fear. I don't want them to be separated for the rest of their natural lives, but am unsure what would have caused this behavior in the first place nor how to resolve it. For the time being I have been giving 2hours in the morning "freedom" runtime for Lucy and Liu and 2 hours in the afternoon for Lucy and Zahra.

I would appreciate any help, advice and information anyone could give me. I tried to find the information on the net but all this behavior seems to be male-dominated (I've checked and double checked to ensure sex). So I'm unsure if this is normal female behavior or if something is wrong.

Thanks in advance.

Cat