Should I confront my mom about money she promised to give me for my wedding?

My sister is 29 years old.She has 3 kids by 3 different guys.She's never been married.She chose not to have a job.She lives off of a combo of food stamps,WIC,child support,& the social security check she receives for her oldest daughter(7) who is deaf.All 3 kids are constantly at their respective grandparents' houses,so she doesn't really take care of them.She's always getting things from people because they feel bad for the kids.I'm about to be 21.I live with my fiance.We both have stable jobs.We're both in school(which we're paying for ourselves).We're also paying for our wedding ourselves.We've paid all our bills ourselves since we moved out when we were 19.My mom said that my parents were going to give us $1000 as a wedding gift,either in cash or to help with the wedding.I initially refused,but she insisted.We budgeted it into the wedding,then after about $200 my mom said she couldn't afford to give us the rest because my sister needs money.Should I confront her about it?