Teacher withholding afternoon snack from Kindergardener because she didnt get her work done

So this is happening to my niece. She is attending a public school where they eat lunch at 10:30am. The teacher asked parents to bring in snacks for the kids to have in the afternoon. My sister has donated lots of healthy snack packs for the students in the afternoon. She just got word yesterday that for the past few weeks my niece hasn't been getting her snack in the afternoon because the teacher said she isn't getting her work done. Now these are snacks... not candies or treats for the kids who excel..

So CC what as re your thoughts? My sister says she has spent $30 so far this year on homeroom snacks and its appealing the teacher is withholding food from them..

The teacher also wanted to fail my niece 5 weeks into the school year because she is "too immature".. when truely she is just extremely shy..