How can my wife who is a Cottage Food owner prepare her tax return? Can we do it jointly with my account?

Yes, you can file a joint return using your account.  Since it sounds like she is a sole proprietor, you can use TurboTax TurboTax Premier to file your return. 

As you walk through the beginning questions, you will tell TurboTax that yes, you have a business and then she will just use her records to enter her income and her expenses. She does not need any tax forms from anyone to file her return. This will generate a Schedule C which is where an individual reports their income and expenses for a small business.  If she has any profit at all from the business, it will also generate a Schedule SE.  This form is for Self-Employment taxes. Her self-employment taxes are 15.3% on her profits. She should be making quarterly payments to avoid penalties.

If she paid anyone more than $600 as a subcontractor or for work done that was not employee work, then she would need to issue those people a 1099-NEC.  If she had employees, then she would need to file W-2's for them. Both the 1099-NEC and the W-2 can be filed through TurboTax Quick Employer Forms.  If she did not pay anyone or have employees, then she would not need to file these forms.