The extent of meaningful advice one can offer here will be greatly limited because it is very fact intensive scenario and will require the proper investigation of facts, etc to arrive at a best course of action.
That said, no, being married does not make her a part of the business automatically and if they are suing her personally my guess is that they are naming the wrong party and she can more than likely get herself dismissed. That is, it sounds as if in this context she is merely just an employee, but alas I am not sure.
I strongly suggest that you consult a lawyer in private and get some insights once you can explain in more detail.
DISCLAIMER: this is not intended to be specific legal advice and should not be relied upon as such. No attorney-client relationship is formed with the law firm of Natoli-Lapin, LLC on the basis of this posting.
I recommend that you consult with a business law attorney in your area. He/she will be able to look at all of the facts of your particular case. Although Avvo is a nice tool for you to ask questions, it is NO substitute for the advise you get from your lawyer assigned to handle your case.
Rengin Bekhtyar's answer to a legal question on Avvo does not establish an attorney-client relationship.
In general, no. If she is not an owner, she would not be liable in the circumstance you describe.
Who is the other owner? (You say is is a sole proprietorship, but use the words "owners." Did you have an owner for the sales transaction?
If you are being sued, you certainly need one now. Hopefully, you can work it out.
If you have been sued, don't mess around trying to get free generalized advice on an online forum. Consult an experienced business attorney. Provide the attorney with a copy of the lawsuit and all of your documentation relating to the formation, operation, and sale of the company. Allow the attorney carefully review your facts and circumstances and provide you with specific advice.
Your question has been answered as a courtesy. This is not paid legal advice. Nothing in this communication is intended to create an attorney-client relationship. Unless expressly stated otherwise, nothing contained in this message should be construed as a digital or electronic signature, nor is it intended to reflect an intention to make an agreement by electronic means.