Our daughter is 15 months old and I think she has croup

She woke up this morning wheezing, then progressed to the seal bark cough and has just been bad throughout the day and got even worse after bed. We did a steamy bathroom and a humidifier in her room. I called the after hours pedi line because it seemed like she was gasping for air during her last fit (an hour ago) but now is sleeping peacefully. Nurse listened to her symptoms and asked me to hold the phone up to DD so she could listen to her breathe. She said to just keep an eye out, call if it seems worse, and call the office for an appointment in the morning. All good advice, but I feel terrible. DD has never been sick except for a cold and seeing her struggling to breathe was awful. She does seem better now, but does anyone know anything else I could do, or words of encouragement?