Hey Guys!
I have two little fur babies Mochi and Tootsie. Tootsie is 2 weeks younger and when I first got her she was very shy and nibbled everything now she is the sweetest thing ever and loves to play and is pretty well bonded and never ever bites me, she is 5 months old now.
Mochi on the other hand I am worried about... She started off as a really sweet glider, very friendly and easy to handle. She is now 5 months and 2 weeks and gets into hissing matches with her sister every night at 3 or so AM (this started about 4 days ago) and when I try to handle her she bites me, hard. She was doing so well when it came to bonding but the like 4 or 5 days ago her personality took a 180 and she is... mean for lack of a better word... I am so worried and confused... nothing has happened so I just don't get it... I took them both to the vet about a month ago and they were perfectly healthy, so unless something change I just dont know...
Any ideas on what could be going on would be helpful, I'm just concerned about my Mochi...

Hi and

They are both still young, but it sounds like one may be in heat to me. They will make hissing noises for a couple of days. My girls have heat cycles at different times and they each make hissing noises in the pouch at this time. I have only one that gets a bit nippy.

Are there any other noticable issues like dinnertime?

I keep blankies(4"×4" pieces of fleece) in their pouch all the time. It gives them something to cuddle with when the other just isn't in the mood to cuddle.
How many sleeping pouches are in the cage at one time?

No issues with dinnertime, they typically just grab some food and run off to opposite ends of the cage anyway when the eat so they dont see much of eachother during meal time. I have 3 pouches in the cage right now normally i have 4 but one got dirty and i have yet to replace it in the cage. They have been sleeping seperate occasionally too which is odd as well because normally they are always sleeping together. If it is her in heat how long does it normally last for? What age do they normally start at?

Dawn is right, one or both may be in heat. They are at the age where they start to cycle.

I would guess heat too. My girls get cranky. The boys also mated a lot even though they are neutered. I would just keep working with her. You may want to take a few steps back in bonding and work back up and it should work out. Arwen gets bitey in heat and Eilonwy gets super curious and adventurous or I just trying to avoid the guys. The boys squabble a little. It mellows a bit with time. Just think of her as an angsty teen and give her a little space but keep working with her.