Weddingbee boards

So my mother in law is someone who is loved by most because she is very sarcastic, cheerful, sweet but i also realize that she has a side to her that is very unpredictable- all of a sudden she would be very quiet, pondering, and kind of sulking.  Sometimes she is very sincere with me, very sweet and I feel like I am so lucky to have someone like that as a MIL.  But then she is also very very sly in that she would say things that would imply something but my fiance would not be able to pick up on them. 

She has done this occasionally in the past and at that moment, I am left stunned as in I can't reply her back because I am left wondering if I am being overanalytical because her other side- the sweet and sincere side makes that unbelievable for me.  But at the same time, when I talk to my friends about the things that she says to me, they think that that is very rude, unacceptable, etc. 

Also, my fiance's family is very well-off.  Sometimes I feel that, based on the things she says, she is trying to make me or my family feel inferior but she says it in such a subtle way that I really feel like trapped.  Because if I say something back, I will be the one who is making it a big deal or being too sensitive about it.  But if I don't say anything, then I am afraid that she will keep doing this in the future and it will be an on-going problem. 

And when I bring these up with my fiance, he is always supportive of his mother and thinks that I am making it a big deal.  However, when it comes to things that he agrees with me about,  he doesn't have the guts to support me against his mother because he is afraid to get her upset or irritated. 

 I really don't know how to handle all of this :(  I don't want to be rude to her, or I don't want to create unnecessary tension but at the same time I don't want her to keep saying these little innocent sounding stuff which are actually quite bothersome.

here is an example:

I'm Turkish and in our tradition, the engagement party is held/organized by the bride's family and the wedding is organized by the groom's family.  When I say organized, I also mean "paid by". 

And for the engagement party, some people do that in their homes, and some people prefer to throw a huge party just like a wedding (150-200 guests).

And neither me nor my fiance wanted a big engagement party, so my parents and I decided to do it in our home. 

A couple of weeks after that, my FMIL was visiting us (my fiance and I live together), and she turns to my fiance and starts telling about this overly fancy and big engagement party she's been to and how she liked that.  Then my fiance said to her, "that is too much,  why would somone throw such a huge party for an engagement?"  Then her answer was "because the bride's parents cared for it".  Then my fiance said "well, we did a very nice engagement party too".  And her answer was "Ours was more like a small gathering, not really an engagement party".

At another time, she tells me that on the wedding day, she would like to take me to the hair salon her best friend always goes to.  And then she added, but not looking directly at me, kind of like trying to test the waters, "But it will be better if your mom and sister don't come because that would be too crowded."  Then I told her, that I want to be with my sister and mom on my wedding day.  Then she laughs, and says "Of course, honey, why would I think otherwise?"  As if she just didn't say that.  And I know that this hair salon is a huge salon, very well-known.  I know it wouldn't be too crowded to go there with 5 people.  After a few minutes, she turns to me "But don't go to that salon in your parents' neighborhood, that is not good enough for a wedding. Maybe it was ok for your engagement party but not for the wedding".   

There are many of these little things that bother me but I kind of avoid to say anything to her because I don't want to cause tension just before the wedding.

@pendola:  Sorry I missed one detail. The problem is, my fiance's dad has cancer since last year, and he is in chemo therapy for the last couple of months. So his mom calls him from time to time, crying, very upset.   So anything that will upset her, he avoids.  But before his illness, there were many occasions that he stood up to his mom to support me or tell her that it is not her business , or that I don't like that or this.....So yeah, that is another issue.  I know that they are going through a hard time emotionally.  So I feel even more reluctant to bring these things up.

@Goldilocks1107:  That is a good advice; I will try that.  At least I will know that when I say that it won't come out as rude but it will put her in the spotlight.