Friend is WAY overstepping.

Hi brides! So, I'm really at a loss about what to do about a friend of mine who has really crossed some boundaries in the last few weeks. My wedding is a low key affair with a very limited guest list. Very close friends and family only. We want to make things as personal and inexpensive as possible so I've asked some artist friends to chip in with decoration and music. One friend in particular is very organised so I asked her to help with the co-ordination of the various artists. She seems to have taken this to mean that she is in charge of my wedding. She has started to tell me (not ask) how the venue and center pieces are going to be decorated. She seems to have totally discounted any potential input from the other artists (one of whom is my sister!) and in a bizarre twist, she convinced her mother (who I barely know) to take time off work to help her decorate the venue. She invited me out for a drink where her and her mom told me of this plan, and made it out like they were doing me a massive favor. I told them I didn't want her to take time off work and it wasn't necessary but she insisted. I was totally blind sided! Now, she has invited her mom not only to my wedding, but to the night before which is supposed to be for bridal party and family. How do I politely tell her to back right on up? She's been a very good friend to me in the past and is currently going though a really tough time mentally so I don't want to be too harsh but I really don't want her taking over my wedding and I REALLY don't want her Mom at my wedding.