Let her buy the fabric, do not use your own fabric. So what if there is extra, that is the nature of quilting and has to be accepted.
My MIL has since passed away, but when she was alive she could suck the life out of you, she never ever went to the store alone, and we live over an hour away, but my husband would get called to the house all the time because she needed something. And then they would go to the drug store and she would buy razors or house shoes. She would give her money to my SIL and then call us cause she needed money, or give my SIL her coat and then call us because she needed a new coat. No one in her home town would help her because she had sucked the life out of every person there. Do what you can and grit your teeth. Remind yourself that you do this for your husband and not for her. Keep saying this is Karma and maybe someday when I am old this will be repaid.