@Kferg Thank you for your reply!
I am planning on taking her to the vet if she does not improve within a week.
Her urine seems fairly normal, no strange smells. The amount she poops is less due to her not eating as much.
She sometimes chirps/hisses when she poops which made me think she's dehydrated so I offer her some apple and/or cranberry juice mixed with water in addition to checking her water and refreshing it often, but I don't know if she's drinking it.
I have put up a barrier between their cages so that they can no longer interact as much. I may move her to another room and restart the introduction process if that doesn't help.
I have tried switching toys between cages. I do "meeting times" where I rub their blankets on each other and let them sniff each other's tails. (The new glider often shivers in her pouch during these and my first glider will grab at the new glider's tail with a bark/crab sound and try to bite it and pull it to her which is usually where I stop the meetings since that's too aggressive) I also try to let them smell the other on me when I've pet/played with the other one. They weren't like this at first, my first glider used to only make a clicking sound of greeting to the new glider but my new one never responded or reacted to it.
I've heard that you should make sure to let the gliders bond before having them bond with you so I wasn't doing regular pouch time with the new glider. I do take her out of her cage from time to time though. I'll try getting her to bond with me by taking her out more often.
My new glider is really sweet and doesn't bite or act aggressive, she does tend to run away from being touched or held though. My first glider loves her pets but she will easily nip at your fingers when she doen't want to be held but it never breaks the skin.