Maybe this is a no brainer, but I'm still confused...
We're throwing a bridal shower for our good friend. It's an all women shower, no men. I don't know how to address the outer envelopes for the married women. For example, I'm married and my husband's name is Martin. Should the outer envelope be:
Mrs. Dianne Naughton then my address or Mrs. Martin Naughton and then my address?
Also, can you tell me if it's okay to use Ms. if I'm unsure if the person has ever been married before?
You could use either Mrs. Diane or Mrs. Martin. However, most women prefer to use their first names, not their husband's. If you are addressing this to an elderly woman or someone very traditional, she probably still uses the husband's first name.
Many women use Ms. whether they are married or not. Actually, I use Ms. and I am very happily married. So many of us would rather be defined as who we are and not by our marital status.