If the block is that out of alignment, won't it affect how the quilt goes together? The seams won't match correctly. Also, the narrow hem may result in a weak spot in the quilt. That one wonky block may affect the look of the entire quilt.
I don't have an easy answer. I guess it depends on how well I know her. My first instinct is to fix her block, and then quietly take her aside and kindly show her what you did. Privately. It sounds like she might be making additional blocks, and you don't want to have this problem again.
I agree with the others - everyone should help with the set up and take down.