Garlic and coconut oil are both anti-fungals. You can make a mouthwash with liquid garlic and use it several times a day. Don't apply garlic directly to your tongue, as it will burn. Mix about 8-10 drops into 8 oz. of water, swish it around your mouth, don't swallow, spit it out.
Coconut oil is great! Swish it around your mouth for about 10 minutes, then spit it out. This is called "oil pulling" and is great for detoxing as well. Also, yogurt fights fungus.
NO SUGAR AT ALL! Fungus feeds on sugar. Smoking also aggravates it, so if she smokes, she might consider quitting and using patches until after the wedding.
Tea tree oil mouthwash
Mix a few drops of tea tree oil (approximately 5 to 8 drops) into a glass of either warm or cold water. Gargle the mixture for about a minute. Let the solution touch all the parts of the mouth (throat, palate, cheek lining). Be careful not to swallow the solution. Gargle two times a day (preferably one in the morning and one before sleeping).
Apple cider vinegar
Mix two (2) teaspoons of apple cider vinegar to one (1) cup cool water. Gargle with solution. Do not swallow. After gargling, dip a cotton swab in undiluted apple cider vinegar and apply directly on to the oral sores. Do not rinse. Allow to stand overnight.