How will you tackle this problem?

A group of people are working on an essay. Each of the three writing members is supposed to write their own parts, put the reference, and submit to the two editing members.

Once they were all done, submitted the report, and met again, the two editing members said triumphantly,

"We found some one of us was committing plagiarism. But fortunately we found out, and we deleted that part that person plagiarized."

All the writing members are totally confused and there is an embarrassing silence in the group.

Later on, the person who "committed plagiarism" found out herself why they said that. She intended to quote the whole paragraph, and put quotation marks at the very beginning, but forgot to put the other half of the quotation marks in the end of the paragraph, although she put the reference there.

She felt so bad, almost burst into tears because she thought the editors should have let her know earlier so that she can review and revise her part… and she might feel not that bad now…

This is a story happened in one of the groups I work with. If you were one of the editors, what would you do if differently?