Etiquette Q: Job Interview Thank You Note, Forms of Adress Therein

Ok, so I had two interviews at a small law firm for a summer job. I want to send thank you notes to the partners who interviewed me for the position.

The firm has 2 partners, a man and a woman. They are married (they told me) and the woman uses her husband’s last name. When addressing the card for the woman, which is more appropriate?:
A. Mrs. X
B. Ms. X

Where X is the surname both share.

I’m leaning towards Ms. X. What say you all?

Ms. Firstname X, definitely. Unless she had something different on her name plate or letterhead.

Regards,
Shodan

Yup, Ms.

I agree, you can’t go wrong with Ms.