Definitely write her a letter. I have problems with my own family and in-laws on certain issues. I've even seen a therapist about it also. My therapist recommended to me to write a letter (less confrontational) when there is a major conflict. My therapist told me some guidelines and I'll pass them on to you:
1.) First draft of letter-write exactly how you feel, get mad and angry, if you need to use bad lanaguage to make you feel better do it. This letter you will not send to the person you are having conflict with. Write was is bothering you and what you would like to see changed and how it makes you feel. Read this letter over and then move on to your second draft of the letter. Feel free to rip up this letter after you've written it.
2.) Second draft- Write a second letter and now tone it down, no bad language, keep rereading your letter. Same rules as the first letter, you will not send it to the person you have a conflict with. write what is bothering you, how you feel, what you want to come out of all this. Cut out things that are disrespectful, mean, hateful, cruel,etc... Read this letter over and after you are done with it, you can throw it away.
3.) Third version- now keep toning it down, keep rereading your letter. You write another letter and read it carefully to make sure it is simple and to the point, the shorter the better. It needs to be respectful, easy to read and something that you wouldn't mind receiving in the mail from a friend/family member if there is a conflict.
4.) You keep doing this over and over, it may take 5 versions of your letter or it may take 7 versions. You may even want your spouse or a friend to read your letter. When you feel comfortable with the final version of your letter, then you can finally send it off to your Mom or who you are having a conflict with.
A letter is much more neutral territory and a smarter way to deal with your anger and frustration with the situation. I've used letters with my Mother-In-Law and my own Mother and I feel so much better afterwards and proud of myself for standing up for myself. Yes, others are right that the person may not change, but things may improve. You never know, why not give her that chance to change or improve? Yes, most older people are set in their ways and don't like much change. At least she will know how you feel about it and that her behavior is disruptive and disrespectful to others.
I'm a Christian also, and I pray about my family also. There are people in this world that we will disagree with and never see eye to eye with them. She may be set in her own ways.
My Mom is obsessive-compulsive and is fixated on how clean our house is when she visits. She lives in another state and only comes 1-2 times a year! I'll admit, we aren't the cleanest house around and I'm the world's worst organizer too! When she visits, she cleans and organizes majority of the time she is visiting us. I've tried getting her out of the house to go to do fun things and it is hard, she doesn't always want a go. I wrote a letter to her about how I was frustrated and upset with how she was dealing with things. I told my counselor and she said my Mom has boundary issues. She recommended me writing the letter and I'm glad I did. It did get my Mom talking to me about it. She verbally talked to me about it and said she thinks our house being messy and dirty is why I am sick a lot. I disagree with her. I just listened to her and bit my tongue and didn't say a word. I did put in my letter that we would have to shorten her visits next time she comes to visit or if she wants to stay longer she can stay in a hotel. I verbally told her on the phone that I didn't want her to clean and organize my closet and things before she was coming down for a visit. She agreed verbally on the phone, however broke her agreement by going back to her old ways. If things don't improve after you write the letter, shorten your trips/visit with her. If family isn't going to be supportive, positive and a healthy environment for you and your family then, take action and spend less time with them. She'll hopefully improve if she wants to spend more time with her grandchildren.
Don't forget it, cause it won't go away or maybe she doesn't realize that she is hurting your feelings. It may be that was the way her Mom talked to her or her Dad talked to her and that may be all she knows what to do. Maybe she will agree to go to counseling or watch what she says and to be more positive and less critical.
I'll keep you in my prayers and I hope it all works out. I dealt with a lot of criticism from my parents. I know what that feels like, it is hard. I had some self-esteem issues, does your husband have any self-esteem issues as a result?
You all may want to go to counseling just to talk about it either as a couple or alone. I have benefited greatly from counseling.
Take care and God Bless.