Here is my take...
I also am married to an 'only son' with overly involved inlaws!!! BTDT!!
Also, the above poster is right. There is a psychological thing going on here where your MIL seems to be living vicariously thru her son and DIL (you). This is NOT good or healthy. But, you really can't do anything about it.
1. You must create your own personal boundaries!!! Your husband must be onboard.... If your MIL wants to copy your hair or your home, etc.. Well, nothing you can do. Remember, imitation is the most sincere form of flattery!!!! Just 'LET IT GO'.
2. Make it almost impossible for her to cross any other lines. She is doing what you have enabled her to do... ( invite her wedding dress shopping... she will become overly involved...) (allow her to handle your wedding gifts, and the top of your wedding cake, she will become overly involved...) etc.. etc.. etc.. etc... etc... You must realize that YOU have been enabling these behaviors, and you must now realize that it is up to YOU to stop setting this stuff up.
3. Your HUSBAND is the one who must handle this, or you will find out really quickly that blood is thicker than water. Your MIL is doing these things to say overly involved in her son's life. She is a parent who simply is not letting go. If it ever appears that it is YOUR doing that there is any pulling away by her son, LOOK OUT. I am giving you a serious warning here. Take heed!!!
Your HUSBAND needs to be the one to handle these things. HE needs to stop by his mother's house and walk out with your wedding cake. You should not say one word, You should not be involved. He should not mention YOUR name.
Your HUSBAND needs to step up the plate here and establish some boundary lines with his mom. I am not talking any big 'discussion' here. But, as I have just described, he should be aware of the situation and actively join with you to NOT make it possible for her to intervene. You both have been enabling her. And, now he must take the lead in not letting these situations even happen.
I totally disagree with the poster who said that a wife should not insist that her husband be on her side and be as one with her and protect her feelings and her interests. If there are husbands who have left their wifes to stay united with their mother, then they were not much of a husband, and it was never a 'marriage' to begin with!!!