Why are my guinea pigs aggression?

I have 2 female guinea pigs who have be caged together for the past year and half. They have gotten along, up til a few days ago. Guinea pig #1 (Moo), keep attacking guinea pig #2 (Lizzie) for no reason at all. Moo chatters her teeth, and sways her hips and then attacks. This morning Moo bit me three times when i tried to separate them. (she have never bitten me before) The only change is that i bought them each an igloo to put by in. I havent changed their diet or anything...so i dont know why Moo is so aggressive towards Lizzie. (they are both about 18 months old..not related to respectively other) I would appreciate any info, or suggestions. Presently, i have them separated in diff cages.
My river frog died, as he hopped...
Answers:    nouns issues can arise as they become more mature and ready to breed. i enjoy found with multiple pets you need to buy one item for each animal. they also could be conflict over the one igloo deal you got both of them. Moo sounds like the pacesetter and is telling Lizzie to back the heck off. you may enjoy to keep them separated unfortunately this is something that won't reverse itself. so sorry hun. good position on taking precautions. best wishes.
What genus of animal should i carry?
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