Ok so maybe try writing down your concerns. Try and keep them short and to the point. I feel.. I dream.. I hope.. I'm sorry.. this is a big one. If anything remorse may be felt by your mom. Even if you don't feel like apologizing, apologize for your outbursts and reactions. Make sure to highlight that your reactions caused by her actions placed you in a feeling of disgust, guilt and embarrassment for the discovery mentioned in your post.

Whatever you do, just remind yourself that there is no book on how to raise children and they are doing their best. I'm not there so I am hoping it is just a strick house as it sounds. Other from that, own your feelings and reach out to your mom in a way that provides distance or mediation, ie a letter while still at grandma's. Maybe even have her write with you or proof read it before sending to mom.