Pen - you are definitely right. Not all situations are the same, and sometimes sons/daughters do pick truly "bad apples." Sometimes the MIL is NOT the issue. Sometimes the DIL is the issue. Sometimes the DIL is not the issue, but her parents are. Sometimes it just simply the environment in which the relationships are bred. Sometimes.....we could go on and on.
But I think Faith really hit the nail on the head, "fear of abondonment." MILs are not the only ones who feel that way, certainly. It affects all parties, and unfortunately leaves usually one person in the middle. Pen - I 've read your post, and I think your DIL is facing that very thing...fear of abandonment (or something very close), and this could be why she has responded to you in the ways she has. Maybe she is jealous of the relationship you have with your son, and she wants to destroy that. Maybe she feels cornered because you make her look bad by being the better person. Maybe she feels like her husband hasn't fully "left" the nest. Who knows why people do the things they do, but it's sad that some people simply don't know how to channel that fear and overcome it so that it doesn't ruin the lives of others. They're the ones who need help dear, not you. But what can you do, besides pray that God have his will. None of us know his reasons for the situations we go through, but we are required to have faith in God that he knows what he's doing and why, and trust that he will not leave us, even at our darkest hour, so hang in there.
But you know, I think I said it before...I could have totally been your DIL. I knew that DH and his mother were close even when we were dating, but I had NO CLUE that he was hiding just how close they were. He was giving her money, paying for her cell phone plan every month, paying her car insurance, and sending her very lavish gifts (a 52-inch flatscreen TV for one!), and funding her beach vacations several times a year. All of this he kept from me, and now he admits that he hid it from me because deep down he knew what a "mama's boy" he would look like if he told me the truth about their relationship. But he says he also knew that if he tried to stop the "money-funnel" to her, she would FLIP OUT. So he just kept doing it and kept it from me. It caused a lot of resentment, especially when it came time to start planning our wedding. I knew how much his job paid him. I knew what bills he had, how much it took to pay them. We had discussed all this when we discussed our "couple" financials and how we would combine our incomes and bills once we were married. But when we started needing to pay for things for our wedding, he was broke. Flat broke. There were times I even had to pay his mortgage for him, even before we lived there together, because he was dry. When I put two-and-two together that his mother was retired and on a fixed income, yet she was taking several lengthy beach vacations every year, then she suddenly got this new television...but she always complained of being broke, I figured out what was going on. I confronted him about it, and intially he lied to me. He was ashamed that he had let himself go broke supporting her lavish lifestyle. I was FURIOUS. It really began to get ugly when we got married, and he suddenly couldn't just send her $1000 without talking to me first, because it was my earnings, my income, my savings now too. And I contributed just as much as he did, actually more. Her "secondary income" suddenly just stopped....and then,
SHE was furious! Suddenly, I was "ruining her relationship" with her son, when in fact, I was just ruining the lifestyle she was used to. Her narcissistic and passive aggressive personality really started to show its ugly head, and we ALL saw her true colors. It was very hard for him not to just give in to her tantrums, just to calm her down, but later on in therapy we resolved that his "pacifying" her was exactly what created that monster, and that it's a temporary solution to a very long-term problem.
Now to my point: I, the DIL, felt abandoned. I felt like his mother was getting the life he'd promised to me. I felt like his loyalty was to HER, even though his vows were spoken to me and to God. So I hastily started acting towards her similarly to how your DIL acts towards you. I made it as uncomfortable as possible for her when she and his father would move into our home for weeks on end. I was downright nasty to them both. I was harboring hatred in my heart towards her, so much that it really began to consume me.
It was wrong. I knew it was wrong, but I felt so "provoked" by her and that's how I justified it. How can a Christian, like I thought I was, be so overcome with hatred? I felt possessed, consumed, and CRAZY!!! And that's when we sought counseling with our pastor. It was there that we peeled back the layers of animosity, and got down to the real "bones" of our problems. It was ALL our faults: MIL's for not allowing her son to emotionally leave the nest, DH's for not "cleaving," and mine too, for reacting to her (and him) out of hatred. We had couples counseling, but I went to pastoral counseling alone as well, just to work through the resentment I had towards them both. In the long run, that's what saved our marriage.
Unfortunately, it didn't save the realtionship between DH and his mother, nor did it improve my own relationship with her. We gave it a try, we invited her to phone counseling with us (she lives several hours away), when she was down visiting other relatives, we made contact with her to try to talk it out, but she couldn't do so without a screaming/cursing fit and tantrum, or her throwing wild accusations towards me. DH eventually just had to cut her off in order to protect his family.
Ok, I'm wrapping up here, I promise!
The real root of our problem we determined was the way WE dealt with the lack of his parents' support of our marriage. It was easy to realize that his mother was throwing us off balance, the hard part was to realize how to deal with it. We desperately wanted his parents' approval and support, but when we didn't get it we reacted badly out of eagerness to gain the approval. In the long run, we couldn't force them to approve and there was nothing we could do to change that except pray for God's will in her life and in ours.