It sounds like she actually may have aspirated some water into her lungs, which can ultimately cause an upper respiratory infections and/or pneumonia, so you need to keep a close eye on her. If the
black beard continues, or if she starts or continues to cough, wheeze, make clicking noises when she breaths, or gets a bunch of excess mucous around her mouth, in strings that you can see when she opens her mouth, then she may need to see a Reptile Vet for a culture.