Be prepared.. kinda long. If I need to fill in blanks, just ask.

My mom took in her best friend, wasn't supposed to be taking in her 19-year old daughter and eventually her daughter came to live there too. Her best friend is in the middle of getting a divorce and her husband told her she had to leave the house. Her daughter smokes weed ((has been to rehab 5 times for various and assorted drugs but comes back every time still smoking weed)) and has been instructed to not bring illegal drugs to my moms house. My mom just got out of an abusive marriage ((physically, emotionally, verbally, mentally, dude went as far as to attempt to kill her three separate times)) where her husband was smoking meth and weed and snorting cocaine in the second story of her house without her knowledge. The one and only rule she had was that weed not be smoked near or in her house. She went on vacation for 5 days and left her best friend and best friend's daughter at her house alone. I went to paint my moms room (that they both knew I was going to do for her while she was gone) and the whole room and bathroom smelled like weed. I was livid. Two days before mom is supposed to get back home and before I've gotten to paint the walls. They have both slept most of the day every day that she has been gone and so it was down to the wire. I kept my mouth shut the first day. Second day, I smelled it in my moms bathroom and on her back porch. When the daughter said that she "should smoke more marijuana" to me, I said, "no, you really probably shouldn't." She said, "you used to be cool about smoking weed." I said, "yeah, until I smelled it IN MY MOM'S HOUSE!" Her response? "Oh shit." I proceeded to unleash the wrath of a thousand suns about how disrespectful it was to do this in my moms house, in the room I'm fixing up for her because she gave up the only bed in the whole house to them and has been sleeping on the couch, etc etc.. she didn't say a word for a while. I went outside to calm down because I was shaking so horribly from being so angry at the disrespect of my mom who took them both in and asked for nothing in return but one simple rule to be followed. When I got back in, she has disappeared and mom's best friend came in and told me not to be mad at her, that she's the one who gave her permission. I then explained the same things to her, disrespectful, wrong, you know moms history and it's the only thing she asked, you knew what I was doing for her while she was gone, etc etc.. both apologized to me. I told my mom the day she was coming home, during a flight delay so that she would have time to cool off before she made it home and smelled it for herself. She was silent. She is so hurt. She's been home two full days now and no one has owned up to what happened while she was gone. Mom is torn. Does she say something even though she shouldn't have to? Does she kick the daughter out? Does she kick them both out? Does she sit them both down and explain how she feels now and let them stay with the promise of it never happening again? Opinions?