I hope this all works out for you, but after reading this post I feel for you. If I were you, I would be setting up some rules about how much control your future MIL has over your life, BEFORE your wedding.
Good Luck
Thanks- yeah, DFiance and I have already talked about this. He hasn't seen his parents since the summer so he felt that he should go out there now (especially since she was giving him a hard time about it). DFiance knows I'm not going to put up with any of this once we are married. I don't feel as if it's my place to have complete control, yet, as we truly aren't married and he is her son, you know? Thanks for the hugs!!
Maybe a similar approach will work for you? Good luck, and ho, ho, ho. She sounds like a pill, your MIL.
I've talked to my MIL about coming out at another time and she says that this is the only time she has room in her house..

. She certainly is a pill but I'm trying to be a good DIL to be, even if it kills me!
Your future MIL is acting like a bully.
Very true-- glad to know I'm just not overreacting.
Has she already purchased the ticket for you to leave this Saturday (the 19th) and returning on the night of the 25th? Does this actually conflict with your exams that you mentioned, or not? Or is it the fact that you will miss seeing your family on the 25th?
Also your fiance is going out there for three weeks? Did you talk to your fiance's mom about this yourself and discuss what dates would be good, or is everything going through him?
As of now she has purchased a single ticket for me to arrive there on the 19th. She is refusing to purchase my home bound ticket until I get out there and we "talk about this".
I have an exam the day before I leave and also have to drive home. So I will be in an exam from 10-12 and then I will be making a 5 hour drive home, alone. The next day my planes leaves at 7am to visit her.
My fiance is going to be out there for 3 weeks- we don't think he'll see them next year except during our wedding (3 days at most) and he doesn't want to deal with her complaining how he never sees them.
I've already told his mom what would work best for me and she doesn't seem to care claiming that it's her way, since she's buying.
I missed the whole DFi thing. You and DFi need to set your boundaries with this woman now -- and get your DFi involved in this. If she's like this from a freakin' plane ticket when you're engaged, what's going to to happen when you have kids?
I know- that's what scares me the most. DFiance and I have already talked about this. We have decided we aren't doing this for the holidays once we are married. We'll alternate between his parents/my parents/and spending Christmas alone until we have kids. Once we have kids, people can come visit us. There's no way in heck I'm taking my littles ones on a 6 hour plane ride everytime she wants to see them.
Going into this marriage, I know I will have my hands full with her. I don't know how to go about setting limits with her NOW since we aren't married yet but once we say "I Do" I plan on doing everything I can to limit the control this woman will try to have over my family
This ...
What do you have scheduled between Saturday and Friday? I wouldn't do it because I wouldn't want to fly across the country on Christmas day ... how is that good for you?
I agree with the previous posters who stated that you need to lay ground rules down BEFORE you get married with this woman. She sounds like she still controls your DFi to a certain extent and is now trying to do it to you. Tell her you appreciate the ticket but it's just not possible for you on such short notice. You NEED to have your DFi on your side for this ... he NEEDS to be out there at home agreeing to your "story." When did you find out that the ticket was for this Saturday? If you knew for a while and are now just deciding it doesn't work then I think you are stuck going ... If she just told you in the last day or two that it was for this weekend and you won't be getting home until 10PM on CHRISTMAS day then you can come up with a 'Story' with your DFi that he agrees to back up and back out of it.
Good Luck ... There is a dance involved when it comes to MIL's and sometimes we have to do things we don't necessarily want for the good of the family and the good of your relationship both with her and your DFi but this is a good time for you to set ground rules not only with her but also with your DFi.
She told me about this plan last week and since then I've been trying to dissuade her. Now she's only bought a one way ticket leaving the 19th so we could decide together when I should leave, whatever that means. All I know is that I will be home for Christmas DAY even if she hates me

.
That being said, thank you for your helpful words!