the best thing to do is have her see her pediatrician. it could be her teeth or another issue like reflux or oral/motor problems. short-term decreases in food intake are usually not a problem but if it's causing her food intake to decrease permanently (or causing food aversions) you need to take action. two year olds cannot always communicate what exactly is going on with them. good luck!
my 27 month old looks like she has all 20 teeth but complains of mouth pain and refuses food what could be problem?