Mother-in-law Hell

We live in a fairly modest house that we haven’t decorated yet because we have both been terribly busy. Now that we have some time off together my fiance suggested that his mom come down and help out. She loves decorating and do it yourself stuff. I thought it would be helpful, we had a lot to do (the entire upstairs) all the painting, trips to the stores and purchasing drawers and night stands. Well, she is here from Saturday through Friday, and all was going well until the day we decided to piece stuff together. I woke up before my fiance because he had a long day at work the day before and asked her if she would like any help putting the new drawers together. She said, right, you can do all the furniture and I’ll do the cleaning. (She wasn’t there for cleaning, she was there to do the furniture stuff… I cleaned the day before.. what she planned on cleaning I don’t know) I looked at the furniture and decided I had better wake my fiance up because I had no idea what I was doing. He woke up and started helping me with the instructions and screws and what not. She heard from downstairs that he had woken up and came running up the stairs telling me I was not mature enough for such a task and I am not smart or posses the skills to do such a little task on my own. I was fuming at that point… we invite her to our home to HELP and she delegates and decides what we’re doing? My fiance just sat there like he hadn’t heard anything and everything was okay. I shut the door with just him and said, your mother cannot treat me like this in our own home. I came out and there she was, listening to the whole conversation.. she screamed at me to GROW UP! All because I needed help piecing something together. My fiance was of no help, saying it was between me and her. The next day while my fiance was at work I was going over what types of food we usually eat on which days (we have a routine and we like it, why change it?) she knows I love chili and that I love my fiances chilli the most and that we only eat it if Steve cooks it. So for lunch today I hear her in the kitchen and come down and there she is, making Chilli, and my fiance wasn’t even home to enjoy it, not to mention I didn’t even eat it.
We are pretty much done with all the tasks around the house, the only thing left is to buy new bedspreads and curtains (something my fiance and I are quite capable of doing ON OUR OWN). My fiance doesn’t see his mother often and she is supposed to be here until Friday well, it is Tuesday and we are all done and there are no more tasks. I don’t have the heart to tell him she has to go, or I am for the next 4 days but it is true. He is working, it isn’t like they are going to spend quality time together. She knows we have a major gala to go to on Saturday and we have many errands to run before it but she insists that traffic will be too bad to leave on Friday, even early in the morning.
I don’t want her around but I also don’t want to upset my fiance…
I’m currently feeling like a prisoner in my own home, I sit in the bedroom until my fiance comes home and then I feel like I’m clinging to him as a safety net… I think she gets the hint but… she just needs to go, this isn’t her vacation and we are done with her help.
What do I do??