Addo has had respiratory disease all his life, but he is VERY healthy according to the vet. He gets batril often and seems to be very happy, he even has a cagemate, Edgar, who isn't affected by this. My vet told me when it was safe to put them together, and they are both happy. They both go for bi-monthly vet checkups just in case.
Do not remove her cagemate. They were already together so the cagemate has already been exposed to whatever she has and if it's just a myco flare up all rats have myco so it doesn't necessarily mean the other rat will have a flare up as well. You can remove her to give her her meds though if the other rat is trying to eat the food containing them. Other than that keep them together because being separated would just make things more stressful for her.
(I copy pasted this from answering the same question of yours in another thread XD)