Can we sue if later we come to find that there were stocks and shares missing that she did not show?

It depends how the release is worded. You should have an attorney review the release. This is opinion is solely based upon the facts presented in the inquiry. Additional facts may be important and may change the analysis. If you are uncertain, seek legal counsel. We are not your attorneys. This answer is being offered to assist you in determining if you need to retain legal counsel to assist you, not to resolve your issue through an email inquiry.