There are two ways to address a female doctor and her husband formally:
If it's a friendly get together then you could address them to each guest as 'This is Dr. Mary Jones and her husband Jack. If...
I think it really depends on the situation. No matter WHAT job she does she will ALWAYS be "Mrs. *First Name* Johnson" OR "Mrs. Ben Johnson." I think the real question here is determined by the...
To address an invitation to a wife who is a doctor it would be: Example: Dr. Jane Doe. The envelope should read Mr. John Doe (if not a doctor of course) & Dr. Jane Doe.