However, if she is talking to you when that class comes in and you happen to be on speaker or she holds the phone in such a way that you can hear and be a witness, and maybe you are on speaker with some others who just happen to be in your office, home, etc., I don't think that would cross any lines, but would give her other witnesses to what the student was saying. May not be a silver bullet, but could be helpful as a support to the document trail your wife is working on.