T.F.
I'm sorry she's going through a tough time.
I'm glad you are seeing Dr's and trying to get this under control.
I am no Dr but does she take a daily allergy pill.. ex Zyrtec, Claritin? I ask because my daughter, never with issues like yours, would have a sinus infection like clockwork in the spring and fall that would knock her on her rear it was so bad.
Testing showed sinus infections and nothing underlying. She started Zyrtec 24 hour daily about 6 years ago and has had a rare pop up of sinus infection until late 2015. Her Dr also recommended switching up by using Zyrtec then Claritin alternately when we needed to start a new bottle so the med is still effective.
Stress also causes illness. Daughter has been sicker (a lot, including heart surgery) since my husband of 26 years, her dad, died suddenly in 2015.
You might also address stress.
Best wishes.