M.P.
If you do not want a direct confrontation I will tell you my story and you can use it to "ask" if she knows anything about it.
Years ago my yahoo email account got "stolen" by a man that knew me, and I am guessing wanted something with me and when he did not get it got very upset.
I did not know what information he had, but apparently he had total access to all my information and contacts. One day my mom calls me very upset because one of her friends received an email from MY email account with a photoshop of me.... in a cover of a men's magazine with huge boobs, totally naked... with my face.
Shortly after a friend called me and said that someone had been chating with him in the yahoo messanger but the messages turned extremely sexually oriented and he knew it could not be me since he knows me from way back.
I cancelled my yahoo account but I do not know how many persons received or lived any type of experience with this person thinking it was me and I can not imagine what could they thought/think of me.
This story can help you.... asking her... have you had any problem with your accounts? did any got hacked or something? my husband received this extremely nasty or disgusting emails and they appear to come from you... ask also infront of your father. She may or may not be brave enough to admit she did it but either way is a way to letting her know you do not like or appreciate this kind of messages to your husband without going full force ready for fight.
Hope this idea helps.
M.