That hidden corner is what would bother me most, because you only found the patch you could finally see. There could easily be more behind the drywall or along the base of the wall where the leak was feeding it for weeks. I’d hand this over to a proper mold remediation service here: http://totalhomerescue.pro/mold-remediation . Have them start with the area behind the cabinet and around the old leak, then work outward from there. I wouldn’t close the wall back up until you know the affected section is actually clean and dry.
