B.C.
I had a cough a few years ago that lingered for 8 weeks.
It was miserable.
Have her use a heating pad on low on her throat and chest over night.
It helped me sleep better.
At 12 yrs old - she's too old for croup anymore - that's for young kids (babies/toddlers/preschoolers) - at 12 her throat air passage should be large enough it can't swell shut anymore.
Have her use a neti pot to rinse her sinuses out with warm saline.
It'll help her rinse allergens out and help keep her nose from dripping down into her lungs.