Is this your first snake? If so, please read
this caresheet on boa constrictors. Now then:
The black bit you see is more than likely her tongue, so don't panic. She isn't going to eat while she continues to be sick, either.
The best thing you can do for her right now, besides continue her medication, is to get her into an enclosure that is 88-90 degrees all the across, no cool side. This will help boost her immune system. Give her a water dish to drink from, but not big enough to soak in. You don't want her to get too much humidity in her enclosure, it needs to be dry so the infection can dry up. Snakes can't cough like we do.
The Baytril may dehydrate her, so expect a really bad shed when she does shed. To help her with that give her a tub she can soak in and mist her every day when she clouds up.
