If I am on antibiotic and steroids I can get yeast (Candida) infection in my mouth. Yeast can be very difficult to get rid off. Diflucan tablets (prescription) is usually prescribed along with Nystatin (prescription) as the drugs of choice. I had to do a few rounds of both after Covid last year. Get off of all sugar....sugar feeds yeast. I also have autoimmune diseases which weakens your immune system. I also take a really good Probiotic. A lof ot times if you have yeast in your mouth or nose, it's in your gut. I take Mega sporebiotic by Microbiome...they are not cheap and you can get them on Amazon or a health food store. Have her talk to her doctor before starting the probiotic. It's very strong and you have to start slow with it. I am so sorry she is battling this.Praying for relief for her. Blessings & Hugs...