My daughter usually also starts with oral Bactrim. If she does not show signs of improvement after 3-4 days she is put on IV's. She has done IV's for up to three weeks. Sometimes it takes that long to clear out her lungs.
Did they do a throat culture on Hailey to see if she's got a new bug? Usually, they will start the patient on an antibiotic that covers what he/she has last cultured. Then they may change the medication if something new shows up on the latest culture.
I recall from the "cough" thread that they thought asthma might be part of the problem. Sometimes my daughter also takes Prednisone (Orapred) before or concurrent with IV's. It is an anti-inflammatory for asthma. It's a steroid with side effects for long term use, but sometimes it has good results if asthma is the culprit.
Good luck and I hope Hailey is feeling better soon.
Maria (mother of three daughters, the youngest, Samantha w/cf)