Is it permissible for female students to participate in purchasing expensive summaries and then photocopying them among themselves, knowing that the seller did not stipulate that they not be copied, and is unaware of this?

There is no objection to benefiting from the book or the summary by sharing it, so that each of you takes turns using it for a few days, or you review it together. As for copying the summary, it is not permissible if its owner prohibits that and it harms him, which is the default, because copyrights and intellectual property rights are private rights for their owners that are recognized by Sharia. If the owner of the summary knows about your sharing and agrees to the copying, then there is no objection. There is an opinion among some scholars that permits copying for personal use without commercial gain, considering it a lesser matter.