Is an agreement between my wife and employer via e-mail with both sides confirming job acceptance considered a Kinyan.
She is going to a din Torah based on this agreement because the employer backed out on the last moment before school started leaving her without a job? what is the source?
The email exchange has the status of a verbal or written conversation, and not of a Kinyan.
Therefore, until your wife actually started working, there is no actual Kinyan, and the theoretical possibility of backing out still exists.
However, it is possible that the Beis Din will decide that the employer owes her compensation on account of the losses incurred by her now being unable for find an alternative position for the coming school year.
Best wishes and good luck.