How big is she/how much does she weigh?
Bigger snakes make noises when they breath that can be confused with a possible respiratory issue.
My female Boa is getting bigger and bigger and is now about 2KG+. When she exerts herself, and if I didn't know better, I would be worried. However, she has no breathing issues and is just a big girl who takes big breathes. When she climbs up my body and her head is near my neck, I hear it a lot louder too.
I had a young snake (Carpet Python - Yafe) who fed ex lost in shipment and had a terrible RI within 24 hours of getting him.
Nasal discharge, mucus in his mouth, whistling and popping, etc. and not on exertion. He also wouldn't eat until the RI was cured.
It sounds to me like she's probably fine, especially if the symptoms are not getting worse.