Im sorry to hear about Macy. It sounds as if she has some major challenges. When a bun is congested like that, it makes it harder for them to eat. And not eating is bad in itself, a you know. It’s possible she her gut is slowed down and became inflammed. The discharge you saw was probably mucus. The gi tract lines itself with mucus as a protective measure.
It’s also possibly the meds she had caused some upset or led to the weird poops. It’s hard to say really.
As intact rabbits are at high risk of developing uterine tumours, be prepared for that. Unfortunately, the common place this will metastasize to is the lungs. That said, her lung condition may be totally unrelated to her being intact. The main thing is doing what you can to help relieve her breathing and if unable to give her quality of life, let her go peacefully.
I hope your visit with the preferred vet gives better idea of what’s going on and a plan of action.
{{{Macy}}}