The filing to end a lawsuit is called a Request for Dismissal, which can be done with or without prejudice. Your mother should consult a lawyer before doing anything, since litigation filings, including voluntarily dismissals of a lawsuit, can have consequences, like owing all these people their costs because they'll be the prevaiing parties in the suit.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
A request for dismissal should not simply be filed to end the suit. Each defendant can then claim costs against her. She needs to get written agreement from each defendant first, that each side will bear their own costs if she dismisses. Then she is protected not only from a cost bill, but potentially a malicious prosecution suit.